Oracle


Oracle Concepts and Architecture Database Structures.

1. What are the components of Physical database structure of Oracle Database?.
ORACLE database is comprised of three types of files. One or more Data files, two are more Redo Log files, and one or more Control files.
2. What are the components of Logical database structure of ORACLE database?
Tablespaces and the Database's Schema Objects.
3. What is a Tablespace?
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.
4. What is SYSTEM tablespace and When is it Created?
Every ORACLE database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.
5. Explain the relationship among Database, Tablespace and Data file.
Each databases logically divided into one or more tablespaces One or more data files are explicitly created for each tablespace.
6. What is schema?
A schema is collection of database objects of a User.
7. What are Schema Objects ?
Schema objects are the logical structures that directly refer to the database's data. Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.
8. Can objects of the same Schema reside in different tablespaces.?
Yes.
9. Can a Tablespace hold objects from different Schemes ?
Yes.
10. what is Table ?
A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.
11. What is a View ?
A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)
12. Do View contain Data ?
Views do not contain or store data.
13. Can a View based on another View ?
Yes.
14. What are the advantages of Views ?
Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table. Hide data complexity. Simplify commands for the user. Present the data in a different perpecetive from that of the base table. Store complex queries.
15. What is a Sequence ?
A sequence generates a serial list of unique numbers for numerical columns of a database's tables.
16. What is a Synonym ?
A synonym is an alias for a table, view, sequence or program unit.
17. What are the type of Synonyms?
There are two types of Synonyms Private and Public.
18. What is a Private Synonyms ?
A Private Synonyms can be accessed only by the owner.
19. What is a Public Synonyms ?
A Public synonyms can be accessed by any user on the database.
20. What are synonyms used for ?
Synonyms are used to : Mask the real name and owner of an object. Provide public access to an object Provide location transparency for tables,views or program units of a remote database. Simplify the SQL statements for database users.
21. What is an Index ?
An Index is an optional structure associated with a table to have direct access to rows,which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.
22. How are Indexes Update ?
Indexes are automatically maintained and used by ORACLE. Changes to table data are automatically incorporated into all relevant indexes.
23. What are Clusters ?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.
24. What is cluster Key ?
The related columns of the tables in a cluster is called the Cluster Key.
25. What is Index Cluster ?
A Cluster with an index on the Cluster Key.
26. What is Hash Cluster ?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.
27. When can Hash Cluster used ?
Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.
28. What is Database Link ?
A database link is a named object that describes a "path" from one database to another.
29. What are the types of Database Links ?
Private Database Link, Public Database Link & Network Database Link.
30. What is Private Database Link ?
Private database link is created on behalf of a specific user. A private database link can be used only when the owner of the link specifies a global object name in a SQL statement or in the definition of the owner's views or procedures.
31. What is Public Database Link ?
Public database link is created for the special user group PUBLIC. A public database link can be used when any user in the associated database specifies a global object name in a SQL statement or object definition.
32. What is Network Database link ?
Network database link is created and managed by a network domain service. A network database link can be used when any user of any database in the network specifies a global object name in a SQL statement or object definition.
33. What is Data Block ?
ORACLE database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.
34. How to define Data Block size ?
A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE datablocks. Block size is specified in INIT.ORA file and cann't be changed latter.

35. What is Row Chaining ?
In Circumstances, all of the data for a row in a table may not be able to fit in the same data block. When this occurs , the data for the row is stored in a chain of data block (one or more) reserved for that segment.
36. What is an Extent ?
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, used to store a specific type of information.
37. What is a Segment ?
A segment is a set of extents allocated for a certain logical structure.
38. What are the different type of Segments ?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.
39. What is a Data Segment ?
Each Non-clustered table has a data segment. All of the table's data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster is stored in the cluster's data segment.
40. What is an Index Segment ?
Each Index has an Index segment that stores all of its data.
41. What is Rollback Segment ?
A Database contains one or more Rollback Segments to temporarily store "undo" information.
42. What are the uses of Rollback Segment ?
Rollback Segments are used : To generate read-consistent database information during database recovery to rollback uncommitted transactions for users.
43. What is a Temporary Segment?
Temporary segments are created by ORACLE when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use.
44. What is a Data File ?
Every ORACLE database has one or more physical data files. A database's data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database.
45. What are the Characteristics of Data Files ?
A data file can be associated with only one database.Once created a data file can't change size.
One or more data files form a logical unit of database storage called a tablespace.
46. What is a Redo Log ?
The set of Redo Log files for a database is collectively known as the database's redo log.
47. What is the function of Redo Log ?
The Primary function of the redo log is to record all changes made to data.
48. What is the use of Redo Log Information ?
The Information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a database's data files.
49. What does a Control file Contain ?
A Control file records the physical structure of the database. It contains the following information.
Database Name, Names and locations of a database's files and redolog files. ,Time stamp of database creation.
50. What is the use of Control File ?
When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.
51. What is a Data Dictionary ?
The data dictionary of an ORACLE database is a set of tables and views that are used as a read-only reference about the database. It stores information about both the logical and physical structure of the database, the valid users of an ORACLE database, integrity constraints defined for tables in the database and space allocated for a schema object and how much of it is being used.
52. What is an Integrity Constrains ?
An integrity constraint is a declarative way to define a business rule for a column of a table.
53. Can an Integrity Constraint be enforced on a table if some existing table data does not satisfy the constraint ?
No.
54. Describe the different type of Integrity Constraints supported by ORACLE ?
NOT NULL Constraint - Disallows NULLs in a table's column. UNIQUE Constraint - Disallows duplicate values in a column or set of columns. PRIMARY KEY Constraint - Disallows duplicate values and NULLs in a column or set of columns. FOREIGN KEY Constrain - Require each value in a column or set of columns match a value in a related table's UNIQUE or PRIMARY KEY. CHECK Constraint - Disallows values that do not satisfy the logical expression of the constraint.
55. What is difference between UNIQUE constraint and PRIMARY KEY constraint ?
A column defined as UNIQUE can contain NULLs while a column defined as PRIMARY KEY can't contain Nulls.
56. Describe Referential Integrity ?
A rule defined on a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). It also specifies the type of data manipulation allowed on referenced data and the action to be performed on dependent data as a result of any action on referenced data.
57. What are the Referential actions supported by FOREIGN KEY integrity constraint ?
UPDATE and DELETE Restrict - A referential integrity rule that disallows the update or deletion of referenced data. DELETE Cascade - When a referenced row is deleted all associated dependent rows are deleted.
58. What is self-referential integrity constraint ?
If a foreign key reference a parent key of the same table is called self-referential integrity constraint.
59. What are the Limitations of a CHECK Constraint ?
The condition must be a Boolean expression evaluated using the values in the row being inserted or updated and can't contain subqueries, sequence, the SYSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.
60. What is the maximum number of CHECK constraints that can be defined on a column ?
No Limit.

SYSTEM ARCHITECTURE :
61. What constitute an ORACLE Instance ?
SGA and ORACLE background processes constitute an ORACLE instance. (or) Combination of memory structure and background process.
62. What is SGA ?
The System Global Area (SGA) is a shared memory region allocated by ORACLE that contains data and control information for one ORACLE instance.
63. What are the components of SGA ?
Database buffers, Redo Log Buffer the Shared Pool and Cursors.
64. What do Database Buffers contain ?
Database buffers store the most recently used blocks of database data. It can also contain modified data that has not yet been permanently written to disk.
65. What do Redo Log Buffers contain ?
Redo Log Buffer stores redo entries a log of changes made to the database.
66. What is Shared Pool ?
Shared Pool is a portion of the SGA that contains shared memory constructs such as shared SQL areas.
67. What is Shared SQL Area ?
A Shared SQL area is required to process every unique SQL statement submitted to a database and contains information such as the parse tree and execution plan for the corresponding statement.
68. What is Cursor ?
A Cursor is a handle ( a name or pointer) for the memory associated with a specific statement.
69. What is PGA ?
Program Global Area (PGA) is a memory buffer that contains data and control information for a server process.
70. What is User Process ?
A user process is created and maintained to execute the software code of an application program. It is a shadow process created automatically to facilitate communication between the user and the server process.
71. What is Server Process ?
Server Process handle requests from connected user process. A server process is in charge of communicating with the user process and interacting with ORACLE carry out requests of the associated user process.
72. What are the two types of Server Configurations ?
Dedicated Server Configuration and Multi-threaded Server Configuration.
73. What is Dedicated Server Configuration ?
In a Dedicated Server Configuration a Server Process handles requests for a Single User Process.
74. What is a Multi-threaded Server Configuration ?
In a Multi-threaded Server Configuration many user processes share a group of server process.
75. What is a Parallel Server option in ORACLE ?
A configuration for loosely coupled systems where multiple instance share a single physical database is called Parallel Server.
76. Name the ORACLE Background Process ?
DBWR - Database Writer. LGWR - Log Writer, CKPT - Check Point, SMON - System Monitor, PMON - Process Monitor, ARCH – Archiver, RECO – Recover, Dnnn - Dispatcher and LCKn – Lock, Snnn - Server.
77. What Does DBWR do ?
Database writer writes modified blocks from the database buffer cache to the data files.
78.When Does DBWR write to the database ?
DBWR writes when more data needs to be read into the SGA and too few database buffers are free. The least recently used data is written to the data files first. DBWR also writes when CheckPoint occurs.
79. What does LGWR do ?
Log Writer (LGWR) writes redo log entries generated in the redo log buffer of the SGA to on-line Redo Log File.
80. When does LGWR write to the database ?
LGWR writes redo log entries into an on-line redo log file when transactions commit and the log buffer files are full.
81. What is the function of checkpoint(CKPT)?
The Checkpoint (CKPT) process is responsible for signaling DBWR at checkpoints and updating all the data files and control files of the database.
82. What are the functions of SMON ?
System Monitor (SMON) performs instance recovery at instance start-up. In a multiple instance system (one that uses the Parallel Server), SMON of one instance can also perform instance recovery for other instance that have failed SMON also cleans up temporary segments that are no longer in use and recovers dead transactions skipped during crash and instance recovery because of file-read or off-line errors. These transactions are eventually recovered by SMON when the tablespace or file is brought back on-line SMON also coalesces free extents within the database to make free space contiguous and easier to allocate.
83. What are functions of PMON ?
Process Monitor (PMON) performs process recovery when a user process fails PMON is responsible for cleaning up the cache and Freeing resources that the process was using PMON also checks on dispatcher and server processes and restarts them if they have failed.
84. What is the function of ARCH ?
Archiver (ARCH) copies the on-line redo log files to archival storage when they are full. ARCH is active only when a database's redo log is used in ARCHIVELOG mode.
85. What is function of RECO ?
RECOver (RECO) is used to resolve distributed transactions that are pending due to a network or system failure in a distributed database. At timed intervals,the local RECO attempts to connect to remote databases and automatically complete the commit or rollback of the local portion of any pending distributed transactions.
86. What is the function of Dispatcher (Dnnn) ?
Dispatcher (Dnnn) process is responsible for routing requests from connected user processes to available shared server processes and returning the responses back to the appropriate user processes.
87. How many Dispatcher Processes are created ?
Atleast one Dispatcher process is created for every communication protocol in use.
88. What is the function of Lock (LCKn) Process ?
Lock (LCKn) are used for inter-instance locking when the ORACLE Parallel Server option is used.
89. What is the maximum number of Lock Processes used ?
Though a single LCK process is sufficient for most Parallel Server systems upto Ten Locks (LCK0,....LCK9) are used for inter-instance locking.

DATA ACCESS
90. Define Transaction ?
A Transaction is a logical unit of work that comprises one or more SQL statements executed by a single user.
91. When does a Transaction end ?
When it is committed or Rollbacked.
92. What does COMMIT do ?
COMMIT makes permanent the changes resulting from all SQL statements in the transaction. The changes made by the SQL statements of a transaction become visible to other user sessions transactions that start only after transaction is committed.
93. What does ROLLBACK do ?
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.
94. What is SAVE POINT ?
For long transactions that contain many SQL statements, intermediate markers or savepoints can be declared which can be used to divide a transaction into smaller parts. This allows the option of later rolling back all work performed from the current point in the transaction to a declared savepoint within the transaction.
95. What is Read-Only Transaction ?
A Read-Only transaction ensures that the results of each query executed in the transaction are consistant with respect to the same point in time.
96. What is the function of Optimizer ?
The goal of the optimizer is to choose the most efficient way to execute a SQL statement.
97. What is Execution Plan ?
The combinations of the steps the optimizer chooses to execute a statement is called an execution plan.
98. What are the different approaches used by Optimizer in choosing an execution plan ?
Rule-based and Cost-based.
99. What are the factors that affect OPTIMIZER in choosing an Optimization approach ?
The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.
100. What are the values that can be specified for OPTIMIZER MODE Parameter ?
COST and RULE.
101. Will the Optimizer always use COST-based approach if OPTIMIZER_MODE is set to "Cost'?
Presence of statistics in the data dictionary for atleast one of the tables accessed by the SQL statements is necessary for the OPTIMIZER to use COST-based approach. Otherwise OPTIMIZER chooses RULE-based approach.
102. What is the effect of setting the value of OPTIMIZER_MODE to 'RULE' ?
This value causes the optimizer to choose the rule_based approach for all SQL statements issued to the instance regardless of the presence of statistics.
103. What are the values that can be specified for OPTIMIZER_GOAL parameter of the ALTER SESSION Command ?
CHOOSE,ALL_ROWS,FIRST_ROWS and RULE.
104. What is the effect of setting the value "CHOOSE" for OPTIMIZER_GOAL, parameter of the ALTER SESSION Command ?
The Optimizer chooses Cost_based approach and optimizes with the goal of best throughput if statistics for atleast one of the tables accessed by the SQL statement exist in the data dictionary. Otherwise the OPTIMIZER chooses RULE_based approach.
105. What is the effect of setting the value "ALL_ROWS" for OPTIMIZER_GOAL parameter of the ALTER SESSION command ?
This value causes the optimizer to the cost-based approach for all SQL statements in the session regardless of the presence of statistics and to optimize with a goal of best throughput.
106. What is the effect of setting the value 'FIRST_ROWS' for OPTIMIZER_GOAL parameter of the ALTER SESSION command ?
This value causes the optimizer to use the cost-based approach for all SQL statements in the session regardless of the presence of statistics and to optimize with a goal of best response time.
107. What is the effect of setting the 'RULE' for OPTIMIER_GOAL parameter of the ALTER SESSION Command ?
This value causes the optimizer to choose the rule-based approach for all SQL statements in a session regardless of the presence of statistics.
108. What is RULE-based approach to optimization ?
Choosing an executing planbased on the access paths available and the ranks of these access paths.
109. What is COST-based approach to optimization ?
Considering available access paths and determining the most efficient execution plan based on statistics in the data dictionary for the tables accessed by the statement and their associated clusters and indexes.

PROGRAMMATIC CONSTRUCTS
110. What are the different types of PL/SQL program units that can be defined and stored in ORACLE database ?
Procedures and Functions,Packages and Database Triggers.
111. What is a Procedure ?
A Procedure consist of a set of SQL and PL/SQL statements that are grouped together as a unit to solve a specific problem or perform a set of related tasks.
112. What is difference between Procedures and Functions ?
A Function returns a value to the caller where as a Procedure does not.
113. What is a Package ?
A Package is a collection of related procedures, functions, variables and other package constructs together as a unit in the database.
114. What are the advantages of having a Package ?
Increased functionality (for example,global package variables can be declared and used by any proecdure in the package) and performance (for example all objects of the package are parsed compiled, and loaded into memory once)
115. What is Database Trigger ?
A Database Trigger is procedure (set of SQL and PL/SQL statements) that is automatically executed as a result of an insert in,update to, or delete from a table.
116. What are the uses of Database Trigger ?
Database triggers can be used to automatic data generation, audit data modifications, enforce complex Integrity constraints, and customize complex security authorizations.
117. What are the differences between Database Trigger and Integrity constraints ?
A declarative integrity constraint is a statement about the database that is always true. A constraint applies to existing data in the table and any statement that manipulates the table. A trigger does not apply to data loaded before the definition of the trigger, therefore, it does not guarantee all data in a table conforms to the rules established by an associated trigger. A trigger can be used to enforce transitional constraints where as a declarative integrity constraint cannot be used.

DATABASE SECURITY
118. What are Roles ?
Roles are named groups of related privileges that are granted to users or other roles.
119. What are the use of Roles ?
REDUCED GRANTING OF PRIVILEGES - Rather than explicitly granting the same set of privileges to many users a database administrator can grant the privileges for a group of related users granted to a role and then grant only the role to each member of the group. DYNAMIC PRIVILEGE MANAGEMENT - When the privileges of a group must change, only the privileges of the role need to be modified. The security domains of all users granted the group's role automatically reflect the changes made to the role. SELECTIVE AVAILABILITY OF PRIVILEGES - The roles granted to a user can be selectively enable (available for use) or disabled (not available for use). This allows specific control of a user's privileges in any given situation.
APPLICATION AWARENESS - A database application can be designed to automatically enable and disable selective roles when a user attempts to use the application.
120. How to prevent unauthorized use of privileges granted to a Role ?
By creating a Role with a password.
121. What is default tablespace ?
The Tablespace to contain schema objects created without specifying a tablespace name.
122. What is Tablespace Quota ?
The collective amount of disk space available to the objects in a schema on a particular tablespace.
123. What is a profile ?
Each database user is assigned a Profile that specifies limitations on various system resources available to the user.
124. What are the system resources that can be controlled through Profile ?
The number of concurrent sessions the user can establish the CPU processing time available to the user's session the CPU processing time available to a single call to ORACLE made by a SQL statement the amount of logical I/O available to the user's session the amout of logical I/O available to a single call to ORACLE made by a SQL statement the allowed amount of idle time for the user's session the allowed amount of connect time for the user's session.
125. What is Auditing ?
Monitoring of user access to aid in the investigation of database use.
126. What are the different Levels of Auditing ?
Statement Auditing, Privilege Auditing and Object Auditing.
127. What is Statement Auditing ?
Statement auditing is the auditing of the powerful system privileges without regard to specifically named objects.
128. What is Privilege Auditing ?
Privilege auditing is the auditing of the use of powerful system privileges without regard to specifically named objects.
129. What is Object Auditing ?
Object auditing is the auditing of accesses to specific schema objects without regard to user.

DISTRIBUTED PROCESSING AND DISTRIBUTED DATABASES
130. What is Distributed database ?
A distributed database is a network of databases managed by multiple database servers that appears to a user as single logical database. The data of all databases in the distributed database can be simultaneously accessed and modified.
131. What is Two-Phase Commit ?
Two-phase commit is mechanism that guarantees a distributed transaction either commits on all involved nodes or rolls back on all involved nodes to maintain data consistency across the global distributed database. It has two phase, a Prepare Phase and a Commit Phase.
132. Describe two phases of Two-phase commit ?
Prepare phase - The global coordinator (initiating node) ask a participants to prepare (to promise to commit or rollback the transaction, even if there is a failure) Commit - Phase - If all participants respond to the coordinator that they are prepared, the coordinator asks all nodes to commit the transaction, if all participants cannot prepare, the coordinator asks all nodes to roll back the transaction.
133. What is the mechanism provided by ORACLE for table replication ?
Snapshots and SNAPSHOT LOGs
134. What is a SNAPSHOT ?
Snapshots are read-only copies of a master table located on a remote node which is periodically refreshed to reflect changes made to the master table.
135. What is a SNAPSHOT LOG ?
A snapshot log is a table in the master database that is associated with the master table. ORACLE uses a snapshot log to track the rows that have been updated in the master table. Snapshot logs are used in updating the snapshots based on the master table.
136. What is a SQL * NET?
SQL *NET is ORACLE's mechanism for interfacing with the communication protocols used by the networks that facilitate distributed processing and distributed databases. It is used in Clint-Server and Server-Server communications.

DATABASE OPERATION, BACKUP AND RECOVERY
137. What are the steps involved in Database Startup ?
Start an instance, Mount the Database and Open the Database.
138. What are the steps involved in Database Shutdown ?
Close the Database, Dismount the Database and Shutdown the Instance.
139. What is Restricted Mode of Instance Startup ?
An instance can be started in (or later altered to be in) restricted mode so that when the database is open connections are limited only to those whose user accounts have been granted the RESTRICTED SESSION system privilege.
140. What are the different modes of mounting a Database with the Parallel Server ?
Exclusive Mode If the first instance that mounts a database does so in exclusive mode, only that Instance can mount the database. Parallel Mode If the first instance that mounts a database is started in parallel mode, other instances that are started in parallel mode can also mount the database.
141. What is Full Backup ?
A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute ORACLE database and the parameter.
142. Can Full Backup be performed when the database is open ?
No.
143. What is Partial Backup ?
A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down.
144.WhatisOn-lineRedoLog?
The On-line Redo Log is a set of tow or more on-line redo files that record all committed changes made to the database. Whenever a transaction is committed, the corresponding redo entries temporarily stores in redo log buffers of the SGA are written to an on-line redo log file by the background process LGWR. The on-line redo log files are used in cyclical fashion.
145. What is Mirrored on-line Redo Log ?
A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks, changes made to one member of the group are made to all members.
146. What is Archived Redo Log ?
Archived Redo Log consists of Redo Log files that have archived before being reused.
147. What are the advantages of operating a database in ARCHIVELOG mode over operating it in NO ARCHIVELOG mode ?
Complete database recovery from disk failure is possible only in ARCHIVELOG mode.
Online database backup is possible only in ARCHIVELOG mode.
148. What is Log Switch ?
The point at which ORACLE ends writing to one online redo log file and begins writing to another is called a log switch.
149. What are the steps involved in Instance Recovery ?
R_olling forward to recover data that has not been recorded in data files, yet has been recorded in the on-line redo log, including the contents of rollback segments. Rolling back transactions that have been explicitly rolled back or have not been committed as indicated by the rollback segments regenerated in step a.  Releasing any resources (locks) held by transactions in process at the time of the failure. Resolving any pending distributed transactions undergoing a two-phase commit at the time of the instance failure.

Data Base Administration
Introduction to DBA
1. What is a Database instance ? Explain
A database instance (Server) is a set of memory structure and background processes that access a set of database files. The process can be shared by all users. The memory structure that are used to store most queried data from database. This helps up to improve database performance by decreasing the amount of I/O performed against data file.
2. What is Parallel Server ?
Multiple instances accessing the same database (Only In Multi-CPU environments)
3. What is a Schema ?
The set of objects owned by user account is called the schema.
4. What is an Index ? How it is implemented in Oracle Database ?
An index is a database structure used by the server to have direct access of a row in a table.
An index is automatically created when a unique of primary key constraint clause is specified in create table comman (Ver 7.0)

5. What is clusters ?
Group of tables physically stored together because they share common columns and are often used together is called Cluster.
6. What is a cluster Key ?
The related columns of the tables are called the cluster key. The cluster key is indexed using a cluster index and its value is stored only once for multiple tables in the cluster.
7. What are the basic element of Base configuration of an oracle Database ?
It consists of one or more data files. one or more control files. two or more redo log files. The Database  contains multiple users/schemas, one or more rollback segments, one or more tablespaces, Data dictionary Tables, User objects (table,indexes,views etc.,), The server that access the database consists of SGA (Database buffer, Dictionary Cache Buffers, Redo log buffers, Shared SQL pool), SMON (System MONito)
PMON (Process MONitor) LGWR (LoG Write) DBWR (Data Base Write) ARCH (ARCHiver) CKPT (Check Point)
RECO Dispatcher, User Process with associated PGS,
8. What is a deadlock ? Explain .
Two processes wating to update the rows of a table which are locked by the other process then deadlock arises. In a database environment this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically. These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally.

MEMORY MANAGEMENT
9. What is SGA ? How it is different from Ver 6.0 and Ver 7.0 ?
The System Global Area in a Oracle database is the area in memory to facilitates the transfer of information between users. It holds the most recently requested structural information between users. It holds the most recently requested structural information about the database. The structure is Database buffers, Dictionary cache, Redo Log Buffer and Shared SQL pool (ver 7.0 only) area.
10. What is a Shared SQL pool ?
The data dictionary cache is stored in an area in SGA called the Shared SQL Pool. This will allow sharing of parsed SQL statements among concurrent users.
11. What is mean by Program Global Area (PGA) ?
It is area in memory that is used by a Single Oracle User Process.
12. What is a data segment ?
Data segment are the physical areas within a database block in which the data associated with tables and clusters are stored.
13. What are the factors causing the reparsing of SQL statements in SGA?
Due to insufficient Shared SQL pool size.
Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio is greater than 1 then increase the SHARED_POOL_SIZE.

LOGICAL & PHYSICAL ARCHITECTURE OF DATABASE.
14. What is Database Buffers ?
Database buffers are cache in the SGA used to hold the data blocks that are read from the data segments in the database such as tables, indexes and clusters DB_BLOCK_BUFFERS parameter in INIT.ORA decides the size.
15. What is dictionary cache ?
Dictionary cache is information about the databse objects stored in a data dictionary table.
16. What is meant by recursive hints ?
Number of times processes repeatedly query the dictionary table is called recursive hints. It is due to the data dictionary cache is too small. By increasing the SHARED_POOL_SIZE parameter we can optimize the size of Data Dictionary Cache.
17. What is meant by redo log buffer ?
Change made to entries are written to the on-line redo log files. So that they can be used in roll forward operations during database recoveries. Before writing them into the redo log files, they will first brought to redo log buffers in SGA and LGWR will write into files frequently. LOG_BUFFER parameter will decide the size.
18. How will you swap objects into a different table space for an existing database ?
Export the user, Perform import using the command imp system/manager file=export.dmp indexfile=newrite.sql. This will create all definitions into newfile.sql. Drop necessary objects.
Run the script newfile.sql after altering the tablespaces. Import from the backup for the necessary objects.
19. List the Optional Flexible Architecture (OFA) of Oracle database ? or How can we organise the tablespaces in Oracle database to have maximum performance ?
SYSTEM - Data dictionary tables. DATA - Standard operational tables. DATA2- Static tables used for standard operations INDEXES - Indexes for Standard operational tables. INDEXES1 - Indexes of static tables used for standard operations. TOOLS - Tools table. TOOLS1 - Indexes for tools table. RBS - Standard Operations Rollback Segments, RBS1,RBS2 - Additional/Special Rollback segments. TEMP - Temporary purpose tablespace TEMP_USER - Temporary tablespace for users. USERS - User tablespace.
20. How will you force database to use particular rollback segment ?
SET TRANSACTION USE ROLLBACK SEGMENT rbs_name.
21. What is meant by free extent ?
A free extent is a collection of continuous free blocks in tablespace. When a segment is dropped its extents are reallocated and are marked as free.
22. How free extents are managed in Ver 6.0 and Ver 7.0 ?
Free extents cannot be merged together in Ver 6.0. Free extents are periodically coalesces with the neighboring free extent in Ver 7.0
23.Which parameter in Storage clause will reduce no. of rows per block?
PCTFREE parameter Row size also reduces no of rows per block.
24. What is the significance of having storage clause ?
We can plan the storage for a table as how much initial extents are required, how much can be extended next, how much % should leave free for managing row updations etc.,
25. How does Space allocation table place within a block ?
Each block contains entries as follows, Fixied block header, Variable block header, Row Header,row date (multiple rows may exists), PCTEREE (% of free space for row updation in future)
26. What is the role of PCTFREE parameter is Storage clause ?
This is used to reserve certain amount of space in a block for expansion of rows.
27. What is the OPTIMAL parameter ?
It is used to set the optimal length of a rollback segment.
28. What is the functionality of SYSTEM table space ?
To manage the database level transactions such as modifications of the data dictionary table that record information about the free space usage.
29. How will you create multiple rollback segments in a database ?
Create a database which implicitly creates a SYSTEM Rollback Segment in a SYSTEM tablespace.
Create a Second Rollback Segment name R0 in the SYSTEM tablespace. Make new rollback segment available (After shutdown, modify init.ora file and Start database) Create other tablespaces (RBS) for rollback segments. Deactivate Rollback Segment R0 and activate the newly created rollback segments.
30. How the space utilisation takes place within rollback segments ?
It will try to fit the transaction in a cyclic fashion to all existing extents. Once it found an extent is in use then it forced to acquire a new extent (No. of extents is based on the optimal size)
31. Why query fails sometimes ?
Rollback segment dynamically extent to handle larger transactions entry loads.
A single transaction may wipeout all avaliable free space in the Rollback Segment Tablespace. This prevents other user using Rollback segments.
32. How will you monitor the space allocation ?
By quering DBA_SEGMENT table/view.
33. How will you monitor rollback segment status ?
Querying the DBA_ROLLBACK_SEGS view, IN USE - Rollback Segment is on-line. AVAILABLE - Rollback Segment available but not on-line. OFF-LINE - Rollback Segment off-line, INVALID - Rollback Segment Dropped. NEEDS RECOVERY - Contains data but need recovery or corupted. PARTLY AVAILABLE - Contains data from an unresolved transaction involving a distributed database.
34. List the sequence of events when a large transaction that exceeds beyond its optimal value when an entry wraps and causes the rollback segment to expand into another extend.
Transaction Begins. An entry is made in the RES header for new transactions entry, Transaction acquires blocks in an extent of RBS The entry attempts to wrap into second extent. None is available, so that the RBS must extent. The RBS checks to see if it is part of its OPTIMAL size. RBS chooses its oldest inactive segment. Oldest inactive segment is eliminated. RBS extents. The Data dictionary table for space management are updated. Transaction Completes. 35. How can we plan storage for very large tables ? Limit the number of extents in the table Separate Table from its indexes. Allocate Sufficient temporary storage.
36. How will you estimate the space required by a non-clustered tables?
Calculate the total header size, Calculate the available dataspace per data block Calculate the combined column lengths of the average row. Calculate the total average row size. Calculate the average number rows that can fit in a block. Calculate the number of blocks and bytes required for the table. After arriving the calculation, add 10 % additional space to calculate the initial extent size for a working table.
37. It is possible to use raw devices as data files and what is the advantages over file. system files ?
Yes. The advantages over file system files. I/O will be improved because Oracle is bye-passing the kernnel which writing into disk. Disk Corruption will be very less.
38. What is a Control file ?
Database's overall physical architecture is maintained in a file called control file. It will be used to maintain internal consistency and guide recovery operations. Multiple copies of control files are advisable.
39. How to implement the multiple control files for an existing database ?
Shutdown the databse. Copy one of the existing control file to new location. Edit Config ora file by adding new control file.name. Restart the database.
40. What is meant by Redo Log file mirrorring ? How it can be achieved?
Process of having a copy of redo log files is called mirroring. This can be achieved by creating group of log files together, so that LGWR will automatically writes them to all the members of the current on-line redo log group. If any one group fails then database automatically switch over to next group. It degrades performance.
41. What is advantage of having disk shadowing/ Mirroring ?
Shadow set of disks save as a backup in the event of disk failure. In most Operating System if any disk failure occurs it automatically switchover to place of failed disk. Improved performance because most OS support volume shadowing can direct file I/O request to use the shadow set of files instead of the main set of files. This reduces I/O load on the main set of disks.
42. What is use of Rollback Segments In Database ?
They allow the database to maintain read consistency between multiple transactions.
43. What is a Rollback segment entry ?
It is the set of before image data blocks that contain rows that are modified by a transaction.
Each Rollback Segment entry must be completed within one rollback segment.
A single rollback segment can have multiple rollback segment entries.
44. What is hit ratio ?
It is a measure of well the data cache buffer is handling requests for data. Hit Ratio = (Logical Reads - Physical Reads - Hits Misses)/ Logical Reads.
45. When will be a segment released ?
When Segment is dropped. When Shrink (RBS only). When truncated (TRUNCATE used with drop storage option).
46. What are disadvanteges of having raw devices ?
We should depend on export/import utility for backup/recovery (fully reliable). The tar command cannot be used for physical file backup, instead we can use dd command which is less flexible and has limited recoveries.
47. List the factors that can affect the accuracy of the estimations ?
The space used transaction entries and deleted records does not become free immediately after completion due to delayed cleanout. Trailling nulls and length bytes are not stored. Inserts of, updates to and deletes of rows as well as columns larger than a single datablock, can cause fragmentation an chained row pieces.

DATABASE SECURITY & ADMINISTRATION
48. What is user Account in Oracle database ?
An user account is not a physical structure in Database but it is having important relationship to the objects in the database and will be having certain privileges.
49. How will you enforce security using stored procedures ?
Don't grant user access directly to tables within the application. Instead grant the ability to access the procedures that access the tables. When procedure executed it will execute the privilege of procedures owner. Users cannot access tables except via the procedure.
50. What are the dictionary tables used to monitor a database spaces ?
DBA_FREE_SPACE, DBA_SEGMENTS, DBA_DATA_FILES.
51. What are the responsibilities of a Database Administrator ?
Installing and upgrading the Oracle Server and application tools. Allocating system storage and planning future storage requirements for the database system. Managing primary database structures (tablespaces). Managing primary objects (table,views,indexes). Enrolling users and maintaining system security. Ensuring compliance with Oralce license agreement. Controlling and monitoring user access to the database. Monitoring and optimising the performance of the database. Planning for backup and recovery of database information. Maintain archived data on tape. Backing up and restoring the database. Contacting Oracle Corporation for technical support.
52. What are the roles and user accounts created automatically with the database ?
DBA - role Contains all database system privileges. SYS user account - The DBA role will be assigned to this account. All of the basetables and views for the database's dictionary are store in this schema and are manipulated only by ORACLE. SYSTEM user account - It has all the system privileges for the database and additional tables and views that display administrative information and internal tables and views used by oracle tools are created using this username.
54. What are the database administrators utilities avaliable ?
SQL * DBA - This allows DBA to monitor and control an ORACLE database. SQL * Loader - It loads data from standard operating system files (Flat files) into ORACLE database tables. Export (EXP) and Import (imp) utilities allow you to move existing data in ORACLE format to and from ORACLE database.
55. What are the minimum parameters should exist in the parameter file (init.ora) ?
DB NAME - Must set to a text string of no more than 8 characters and it will be stored inside the datafiles, redo log files and control files and control file while database creation. DB_DOMAIN - It is string that specifies the network domain where the database is created. The global database name is identified by setting these parameters (DB_NAME & DB_DOMAIN)
CONTORL FILES - List of control filenames of the database. If name is not mentioned then default name will be used. DB_BLOCK_BUFFERS - To determine the no of buffers in the buffer cache in SGA. PROCESSES - To determine number of operating system processes that can be connected to ORACLE concurrently. The value should be 5 (background process) and additional 1 for each user. ROLLBACK_SEGMENTS - List of rollback segments an ORACLE instance acquires at database startup. Also optionally LICENSE_MAX_SESSIONS,LICENSE_SESSION_WARNING and LICENSE_MAX_USERS.
56. What is a trace file and how is it created ?
Each server and background process can write an associated trace file. When an internal error is detected by a process or user process, it dumps information about the error to its trace. This can be used for tuning the database.
57. What are roles ? How can we implement roles ?
Roles are the easiest way to grant and manage common privileges needed by different groups of database users. Creating roles and assigning provies to roles. Assign each role to group of users. This will simplify the job of assigning privileges to individual users.
58. What are the steps to switch a database's archiving mode between NO ARCHIVELOG and ARCHIVELOG mode ?
1. Shutdown the database instance. 2. Backup the databse. 3. Perform any operating system specific steps (optional). 4. Start up a new instance and mount but do not open the databse. 5. Switch the databse's archiving mode.
59. How can you enable automatic archiving ?
Shut the database. Backup the database. Modify/Include LOG_ARCHIVE_START_TRUE in init.ora file. Start up the databse.
60. How can we specify the Archived log file name format and destination ?
By setting the following values in init.ora file. LOG_ARCHIVE_FORMAT = arch %S/s/T/tarc (%S - Log sequence number and is zero left paded, %s - Log sequence number not padded. %T - Thread number lef-zero-paded and %t - Thread number not padded). The file name created is arch 0001 are if %S is used. LOG_ARCHIVE_DEST = path.
61. What is the use of ANALYZE command ?
To perform one of these function on an index,table, or cluster: - to collect statisties about object used by the optimizer and store them in the data dictionary. - to delete statistics about the object used by object from the data dictionary. - to validate the structure of the object. - to identify migrated and chained rows of the table or cluster.

MANAGING DISTRIBUTED DATABASES.
62. How can we reduce the network traffic ?
Replictaion of data in distributed environment. Using snapshots to replicate data. Using remote procedure calls.
63. What is snapshots ?
Snapshot is an object used to dynamically replicate data between distribute database at specified time intervals. In ver 7.0 they are read only.
64. What are the various type of snapshots ?
Simple and Complex.
65. Differentiate simple and complex, snapshots ?
A simple snapshot is based on a query that does not contains GROUP BY clauses, CONNECT BY clauses, JOINs, sub-query or snashot of operations. A complex snapshots contain atleast any one of the above.
66. What dynamic data replication ?
Updating or Inserting records in remote database through database triggers. It may fail if remote database is having any problem.
67. How can you Enforce Refrencial Integrity in snapshots ?
Time the references to occur when master tables are not in use. Peform the reference the manually immdiately locking the master tables. We can join tables in snopshots by creating a complex snapshots that will based on the master tables.
68. What are the options available to refresh snapshots ?
COMPLETE - Tables are completly regenerated using the snapshot's query and the master tables every time the snapshot referenced. FAST - If simple snapshot used then a snapshot log can be used to send the changes to the snapshot tables. FORCE - Default value. If possible it performs a FAST refresh; Otherwise it will perform a complete refresh.
69. what is snapshot log ?
It is a table that maintains a record of modifications to the master table in a snapshot. It is stored in the same database as master table and is only available for simple snapshots. It should be created before creating snapshots.
70. When will the data in the snapshot log be used ?
We must be able to create a after row trigger on table (i.e., it should be not be already available )
After giving table privileges. We cannot specify snapshot log name because oracle uses the name of the master table in the name of the database objects that support its snapshot log. The master table name should be less than or equal to 23 characters. (The table name created will be MLOGS_tablename, and trigger name will be TLOGS name).
72. What are the benefits of distributed options in databases ?
Database on other servers can be updated and those transactions can be grouped together with others in a logical unit. Database uses a two phase commit.

MANAGING BACKUP & RECOVERY
73. What are the different methods of backing up oracle database ?
- Logical Backups - Cold Backups - Hot Backups (Archive log)
74. What is a logical backup ?
Logical backup involves reading a set of databse records and writing them into a file. Export utility is used for taking backup and Import utility is used to recover from backup.
75. What is cold backup ? What are the elements of it ?
Cold backup is taking backup of all physical files after normal shutdown of database. We need to take.
- All Data files. - All Control files. - All on-line redo log files. - The init.ora file (Optional)
76. What are the different kind of export backups ?
Full back - Complete database. Incremental - Only affected tables from last incremental date/full backup date. Cumulative backup - Only affected table from the last cumulative date/full backup date.
77. What is hot backup and how it can be taken ?
Taking backup of archive log files when database is open. For this the ARCHIVELOG mode should be enabled. The following files need to be backed up.  All data files. All Archive log, redo log files. All control files.
78. What is the use of FILE option in EXP command ?
To give the export file name.
79. What is the use of COMPRESS option in EXP command ?
Flag to indicate whether export should compress fragmented segments into single extents.
80. What is the use of GRANT option in EXP command ?
A flag to indicate whether grants on databse objects will be exported or not. Value is 'Y' or 'N'.
81. What is the use of INDEXES option in EXP command ?
A flag to indicate whether indexes on tables will be exported.
82. What is the use of ROWS option in EXP command ?
Flag to indicate whether table rows should be exported. If 'N' only DDL statements for the databse objects will be created.
83. What is the use of CONSTRAINTS option in EXP command ?
A flag to indicate whether constraints on table need to be exported.

84. What is the use of FULL option in EXP command ?
A flag to indicate whether full databse export should be performed.
85. What is the use of OWNER option in EXP command ?
List of table accounts should be exported.
86. What is the use of TABLES option in EXP command ?
List of tables should be exported.
87. What is the use of RECORD LENGTH option in EXP command ?
Record length in bytes.
88. What is the use of INCTYPE option in EXP command ?
Type export should be performed COMPLETE,CUMULATIVE,INCREMENTAL.
89. What is the use of RECORD option in EXP command ?
For Incremental exports, the flag indirects whether a record will be stores data dictionary tables recording the export.
90. What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.
91. What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.
92. What is the use of ANALYSE ( Ver 7) option in EXP command ?
A flag to indicate whether statistical information about the exported objects should be written to export dump file.
93. What is the use of CONSISTENT (Ver 7) option in EXP command ?
A flag to indicate whether a read consistent version of all the exported objects should be maintained.
94. What is use of LOG (Ver 7) option in EXP command ?
The name of the file which log of the export will be written.
95.What is the use of FILE option in IMP command ?
The name of the file from which import should be performed.
96. What is the use of SHOW option in IMP command ?
A flag to indicate whether file content should be displayed or not.
97. What is the use of IGNORE option in IMP command ?
A flag to indicate whether the import should ignore errors encounter when issuing CREATE commands.
98. What is the use of GRANT option in IMP command ?
A flag to indicate whether grants on database objects will be imported.
99. What is the use of INDEXES option in IMP command ?
A flag to indicate whether import should import index on tables or not.
100. What is the use of ROWS option in IMP command ?
A flag to indicate whether rows should be imported. If this is set to 'N' then only DDL for database objects will be exectued.

SQL PLUS STATEMENTS
1. What are the types of SQL Statement ?
Data Definition Language : CREATE,ALTER,DROP,TRUNCATE,REVOKE,NO AUDIT & COMMIT.
Data Manipulation Language : INSERT,UPDATE,DELETE,LOCK TABLE,EXPLAIN PLAN & SELECT.
Transactional Control : COMMIT & ROLLBACK. Session Control : ALTERSESSION & SET ROLE. System Control : ALTER SYSTEM.
2. What is a transaction ?
Transaction is logical unit between two commits and commit and rollback.
3. What is difference between TRUNCATE & DELETE ?
TRUNCATE commits after deleting entire table i.e., can not be rolled back. Database triggers do not fire on TRUNCATE, DELETE allows the filtered deletion. Deleted records can be rolled back or committed. Database triggers fire on DELETE.
4. What is a join ? Explain the different types of joins ?
Join is a query which retrieves related columns or rows from multiple tables. Self Join - Joining the table with itself. Equi Join - Joining two tables by equating two common columns. Non-Equi Join - Joining two tables by equating two common columns. Outer Join - Joining two tables in such a way that query can also retrive rows that do not have corresponding join value in the other table.
5. What is the Subquery ?
Subquery is a query whose return values are used in filtering conditions of the main query.
6. What is correlated sub-query ?
Correlated sub_query is a sub_query which has reference to the main query.
7. Explain Connect by Prior ?
Retrives rows in hierarchical order.
e.g. select empno, ename from emp where.
8. Difference between SUBSTR and INSTR ?
INSTR (String1,String2(n,(m)), INSTR returns the position of the mth occurrence of the string 2 in
string1. The search begins from nth position of string1. SUBSTR (String1 n,m) SUBSTR returns a character string of size m in string1, starting from nth postion of string1.
9. Explain UNION,MINUS,UNION ALL, INTERSECT ?
INTERSECT returns all distinct rows selected by both queries. MINUS - returns all distinct rows selected by the first query but not by the second. UNION - returns all distinct rows selected by either query. UNION ALL - returns all rows selected by either query,including all duplicates.
10. What is ROWID ?
ROWID is a pseudo column attached to each row of a table. It is 18 character long, blockno, rownumber are the components of ROWID.
11. What is the fastest way of accessing a row in a table ?
Using ROWID.

CONSTRAINTS
12. What is an Integrity Constraint ?
Integrity constraint is a rule that restricts values to a column in a table.
13. What is Referential Integrity ?
Maintaining data integrity through a set of rules that restrict the values of one or more columns of the tables based on the values of primary key or unique key of the referenced table.
14. What are the usage of SAVEPOINTS ?
SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling back part of a transaction. Maximum of five save points are allowed.
15. What is ON DELETE CASCADE ?
When ON DELETE CASCADE is specified ORACLE maintains referential integrity by automatically removing dependent foreign key values if a referenced primary or unique key value is removed.
16. What are the data types allowed in a table ?
CHAR,VARCHAR2,NUMBER,DATE,RAW,LONG and LONG RAW.
17. What is difference between CHAR and VARCHAR2 ? What is the maximum SIZE allowed for each type ?
CHAR pads blank spaces to the maximum length. VARCHAR2 does not pad blank spaces. For CHAR it is 255 and 2000 for VARCHAR2.
18. How many LONG columns are allowed in a table ? Is it possible to use LONG columns in WHERE clause or ORDER BY ?
Only one LONG columns is allowed. It is not possible to use LONG column in WHERE or ORDER BY clause.
19. What are the pre requisites ?
To modify datatype of a column. To add a column with NOT NULL constraint. To Modify the datatype of a column the column must be empty. to add a column with NOT NULL constrain, the table must be empty.
20. Where the integrity constrints are stored in Data Dictionary ?
The integrity constraints are stored in USER_CONSTRAINTS.
21. How will you a activate/deactivate integrity constraints ?
The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE constraint/DISABLE constraint.
22. If an unique key constraint on DATE column is created, will it validate the rows that are inserted with SYSDATE ?
It won't, Because SYSDATE format contains time attached with it.
23. What is a database link ?
Database Link is a named path through which a remote database can be accessed.
24. How to access the current value and next value from a sequence ? Is it possible to access the current value in a session before accessing next value ?
Sequence name CURRVAL, Sequence name NEXTVAL. It is not possible. Only if you access next value in the session, current value can be accessed.
25. What is CYCLE/NO CYCLE in a Sequence ?
CYCLE specifies that the sequence continues to generate values after reaching either maximum or minimum value. After pan ascending sequence reaches its maximum value, it generates its minimum value. After a descending sequence reaches its minimum, it generates its maximum. NO CYCLE specifies that the sequence cannot generate more values after reaching its maximum or minimum value.
26. What are the advantages of VIEW ?
To protect some of the columns of a table from other users. To hide complexity of a query. To hide complexity of calculations.
27. Can a view be updated/inserted/deleted? If Yes under what conditions ?
A View can be updated/deleted/inserted if it has only one base table if the view is based on columns from one or more tables then insert, update and delete is not possible.
28.If a View on a single base table is manipulated will the changes be reflected on the base table ?
If changes are made to the tables which are base tables of a view will the changes be reference on the view.

Datatypes PL/SQL
5. What are the datatypes a available in PL/SQL ?
Some scalar data types such as NUMBER, VARCHAR2, DATE, CHAR, LONG, BOOLEAN. Some composite data types such as RECORD & TABLE.
6. What are % TYPE and % ROWTYPE ? What are the advantages of using these over datatypes?
% TYPE provides the data type of a variable or a database column to that variable. % ROWTYPE provides the record type that represents a entire row of a table or view or columns selected in the cursor.
The advantages are : I. Need not know about variable's data type ii. If the database definition of a column in a table changes, the data type of a variable changes accordingly.
7. What is difference between % ROWTYPE and TYPE RECORD ?
% ROWTYPE is to be used whenever query returns a entire row of a table or view. TYPE rec RECORD is to be used whenever query returns columns of different table or views and variables. E.g. TYPE r_emp is RECORD (eno emp.empno% type,ename emp ename %type); e_rec emp% ROWTYPE;
cursor c1 is select empno,deptno from emp; e_rec c1 %ROWTYPE.
8. What is PL/SQL table ?
Objects of type TABLE are called "PL/SQL tables", which are modelled as (but not the same as) database tables, PL/SQL tables use a primary PL/SQL tables can have one column and a primary key.

Cursors
9. What is a cursor ? Why Cursor is required ?
Cursor is a named private SQL area from where information can be accessed. Cursors are required to process rows individually for queries returning multiple rows.
10. Explain the two type of Cursors ?
There are two types of cursors, Implict Cursor and Explicit Cursor. PL/SQL uses Implict Cursors for queries.
User defined cursors are called Explicit Cursors. They can be declared and used.
11. What are the PL/SQL Statements used in cursor processing ?
DECLARE CURSOR cursor name, OPEN cursor name, FETCH cursor name INTO or Record types, CLOSE cursor name.
12. What are the cursor attributes used in PL/SQL ?
%ISOPEN - to check whether cursor is open or not. % ROWCOUNT - number of rows featched/updated/deleted. % FOUND - to check whether cursor has fetched any row. True if rows are featched. % NOT FOUND - to check whether cursor has featched any row. True if no rows are featched. These attributes are proceded with SQL for Implict Cursors and with Cursor name for Explict Cursors.
13. What is a cursor for loop ?
Cursor for loop implicitly declares %ROWTYPE as loop index,opens a cursor, fetches rows of values from active set into fields in the record and closes when all the records have been processed. eg. FOR emp_rec IN C1 LOOP salary_total := salary_total +emp_rec sal; END LOOP;
14. What will happen after commit statement ?
Cursor C1 is Select empno, ename from emp; Begin open C1; loop Fetch C1 into eno.ename; Exit When C1 %notfound;-----commit; end loop; end;
The cursor having query as SELECT .... FOR UPDATE gets closed after COMMIT/ROLLBACK.
The cursor having query as SELECT.... does not get closed even after COMMIT/ROLLBACK.

15. Explain the usage of WHERE CURRENT OF clause in cursors ?
WHERE CURRENT OF clause in an UPDATE,DELETE statement refers to the latest row fetched from a cursor. Database Triggers
16. What is a database trigger ? Name some usages of database trigger ?
Database trigger is stored PL/SQL program unit associated with a specific database table. Usages are Audit data modificateions, Log events transparently, Enforce complex business rules Derive column values automatically, Implement complex security authorizations. Maintain replicate tables.
17. How many types of database triggers can be specified on a table ? What are they ?
Insert Update Delete. Before Row o.k. o.k. o.k. After Row o.k. o.k. o.k. Before Statement o.k. o.k.  o.k. After Statement o.k. o.k. o.k. If FOR EACH ROW clause is specified, then the trigger for each Row affected by the statement. If WHEN clause is specified, the trigger fires according to the retruned boolean value.
18. Is it possible to use Transaction control Statements such a ROLLBACK or COMMIT in Database Trigger ? Why ?
It is not possible. As triggers are defined for each table, if you use COMMIT of ROLLBACK in a trigger, it affects logical transaction processing.
19. What are two virtual tables available during database trigger execution ?
The table columns are referred as OLD.column_name and NEW.column_name. For triggers related to INSERT only NEW.column_name values only available. For triggers related to UPDATE only OLD.column_name NEW.column_name values only available. For triggers related to DELETE only OLD.column_name values only available.
20. What happens if a procedure that updates a column of table X is called in a database trigger of the same table ?
Mutation of table occurs.
21. Write the order of precedence for validation of a column in a table ?
I. done using Database triggers. ii. done using Integarity Constraints. I & ii.

Exception :
22. What is an Exception ? What are types of Exception ?
Exception is the error handling part of PL/SQL block. The types are Predefined and user_defined. Some of Predefined execptions are.  CURSOR_ALREADY_OPEN. DUP_VAL_ON_INDEX. NO_DATA_FOUND. TOO_MANY_ROWS. INVALID_CURSOR. INVALID_NUMBER. LOGON_DENIED. NOT_LOGGED_ON. PROGRAM-ERROR. STORAGE_ERROR. TIMEOUT_ON_RESOURCE. VALUE_ERROR. ZERO_DIVIDE. OTHERS.
23. What is Pragma EXECPTION_INIT ? Explain the usage ?
The PRAGMA EXECPTION_INIT tells the complier to associate an exception with an oracle error. To get an error message of a specific oracle error. e.g. PRAGMA EXCEPTION_INIT (exception name, oracle error number)
24. What is Raise_application_error ?
Raise_application_error is a procedure of package DBMS_STANDARD which allows to issue an user_defined error messages from stored sub-program or database trigger.
25. What are the return values of functions SQLCODE and SQLERRM ?
SQLCODE returns the latest code of the error that has occured. SQLERRM returns the relevant error message of the SQLCODE.
26. Where the Pre_defined_exceptions are stored ?
In the standard package.

Procedures, Functions & Packages ;
27. What is a stored procedure ?
A stored procedure is a sequence of statements that perform specific function.
28. What is difference between a PROCEDURE & FUNCTION ?
A FUNCTION is alway returns a value using the return statement. A PROCEDURE may return one or more values through parameters or may not return at all.
29. What are advantages fo Stored Procedures /
Extensibility,Modularity, Reusability, Maintainability and one time compilation.
30. What are the modes of parameters that can be passed to a procedure ?
IN,OUT,IN-OUT parameters.
31. What are the two parts of a procedure ?
Procedure Specification and Procedure Body.
32. Give the structure of the procedure ?
PROCEDURE name (parameter list.....) is local variable declarations BEGIN Executable statements.
Exception. exception handlers end;
33. Give the structure of the function ?
FUNCTION name (argument list .....) Return datatype is local variable declarations Begin executable statements Exception execution handlers End;
34. Explain how procedures and functions are called in a PL/SQL block ?
Function is called as part of an expression. sal := calculate_sal ('a822'); procedure is called as a PL/SQL statement calculate_bonus ('A822');
35. What is Overloading of procedures ?
The Same procedure name is repeated with parameters of different datatypes and parameters in different positions, varying number of parameters is called overloading of procedures.
e.g. DBMS_OUTPUT put_line
36. What is a package ? What are the advantages of packages ?
Package is a database object that groups logically related procedures. The advantages of packages are Modularity, Easier Applicaton Design, Information. Hiding,. reusability and Better Performance.
37.What are two parts of package ?
The two parts of package are PACKAGE SPECIFICATION & PACKAGE BODY.
Package Specification contains declarations that are global to the packages and local to the schema. Package Body contains actual procedures and local declaration of the procedures and cursor declarations.
38. What is difference between a Cursor declared in a procedure and Cursor declared in a package specification ?
A cursor declared in a package specification is global and can be accessed by other procedures or procedures in a package. A cursor declared in a procedure is local to the procedure that can not be accessed by other procedures.
39. How packaged procedures and functions are called from the following?
a. Stored procedure or anonymous block b. an application program such a PRC *C, PRO* COBOL, c. SQL *PLUS
a. PACKAGE NAME.PROCEDURE NAME (parameters);
variable := PACKAGE NAME.FUNCTION NAME (arguments);
EXEC SQL EXECUTE
b. BEGIN
PACKAGE NAME.PROCEDURE NAME (parameters)
variable := PACKAGE NAME.FUNCTION NAME (arguments);
END;
END EXEC;
c. EXECUTE PACKAGE NAME.PROCEDURE if the procedures does not have any
out/in-out parameters. A function can not be called.

40. Name the tables where characteristics of Package, procedure and functions are stored ?
User_objects, User_Source and User_error.

DBA

1.     What DBA activities did you to do today?

Wow, this is a loaded question and almost begs for you to answer it with "What DBA activities do you LIKE to do on a daily basis?." And that is how I would answer this question. Again, do not get caught up in the "typical" day-to-day operational issues of database administration. Sure, you can talk about the index you rebuilt, the monitoring of system and session waits that were occurring, or the space you added to a data file, these are all good and great and you should convey that you understand the day-to-day operational issues. What you should also throw into this answer are the meetings that you attend to provide direction in the database arena, the people that you meet and talk with daily to answer adhoc questions about database use, the modeling of business needs within the database, and the extra time you spend early in the morning or late at night to get the job done. Just because the question stipulates "today" do not take "today" to mean "today." Make sure you wrap up a few good days into "today" and talk about them. This question also begs you to ask the question of "What typical DBA activities are performed day to day within X Corporation?"
2.     What is your typical day like?
If you spend enough time on question 1, this question will never be asked. It is really a continuation of question 1 to try and get you to open up and talk about the type of things you like to do. Personally, I would continue with the theme of question 1 if you are cut short or this question is asked later in the interview process. Just note that this question is not all geared toward the day-to-day operational issues you experience as a DBA. This question also gives you the opportunity to see if they want to know about you as an individual. Since the question did not stipulate "on the job" I would throw in a few items like, I get up at 5:00am to get into work and get some quiet time to read up on new trends or you help coach your son/daughter's soccer team. Just test the waters to what is acceptable. If the interviewer starts to pull you back to "job" related issues, do not go to personal. Also, if you go to the office of the interviewer please notice the surroundings, if there are pictures of his/her family, it is probably a good idea to venture down the personal path. If there is a fly-fishing picture on the wall, do not say you like deep-sea fishing. You get the picture.
3.     What other parts of your organization do you interact with and how?
Again, if you have exhausted question 1 and 2 you may never get to this question. But if you have been apprehensive to opening up and explaining yourself, take note that you may have an issue and the interviewer might also be already getting tired of the interview process. If you get to this question consider yourself in trouble. You really need to forget all your hang-ups and start explaining what it is that you like to do as a DBA, and why you want to work for this particular company. You are going to have to reel this interviewer back into the interview process or you might not get to the true technical question part of the interview.
4.     Do you consider yourself a development DBA or a production DBA and why?
I take this as a trick question and explain it that way. Never in my database carrier have I distinguished between "development" and "production." Just ask your development staff or VP of engineering how much time and money is lost if development systems are down. Explain to the interviewer that both systems are equally important to the operation of the company and both should be considered as production systems because there are people relying on them and money is lost if either one of them is down. Ok you may be saying, and I know you are, that we lose more money if the production system is down. Ok, convey that to the interviewer and you won't get anyone to disagree with you unless your company sells software or there are million dollar deals on the table that are expecting the next release of your product or service.
5.     Are you a nuts-n-bolts DBA or a tools-n-props DBA
This question begs for me to give definition around the terms I basically group DBAs into. These are not good or bad groups but something I like to think about when talking to DBAs. A nuts-n-bolts DBA is the type that likes to figure out every little item about how the database works. He/she is a DBA who typically hates a GUI environment and prefers the command line to execute commands and accomplish tasks. A nuts-n-bolts DBA like to feel in control of the database and only feels comfortable at the command line and vi as an editor. The tools-n-props DBA is mostly the opposite of a nuts-n-bolts DBA, they like the feel of a GUI, the ease at which things can be accomplished without knowing much about the database. They want to get the job done with the least amount of intervention from having to figure out what everything is doing behind the scenes. Now the answer, I would explain myself as a combination of the two. I, having been in this business for over 20 years, have grown up in a command line era where the GUIs never seemed to work. There was high complexity in systems and not much good documentation on how things worked. Thus, I had to learn everything about most aspects of the database environment I was working in and thus became a nuts-n-bolts DBA. I was a true command line and vi bigot. Times have changed and the GUIs are very reliable, understand the environment they are installed on, and can generally get the job done quicker for individuals new to database administration. I too am slowly slipping over to the dark side of GUI administration. If you find yourself as a tools-n-props DBA, try to convey that you are aware of some tasks that require you to be a nuts-n-bolts DBA.

Technical Oracle
1.     Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any point in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk.
2.     You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause.
3.     How do you switch from an init.ora file to a spfile?
Issue the create spfile from pfile command.
4.     Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
5.     Give two examples of how you might determine the structure of the table DEPT.
Use the describe command or use the dbms_metadata.get_ddl package.
6.     Where would you look for errors from the database engine?
In the alert log.
7.     Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.
8.     Give the reasoning behind using an index.
Faster access to data blocks in a table.
9.     Give the two types of tables involved in producing a star schema and the type of data they hold.
Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables.
10. . What type of index should you use on a fact table?
A Bitmap index.
11. Give two examples of referential integrity constraints.
A primary key and a foreign key.
12. A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables?
Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint.
13. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any point in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.
14. What command would you use to create a backup control file?
Alter database backup control file to trace.
15. Give the stages of instance startup to a usable state where normal users may access it.
STARTUP NOMOUNT - Instance startup
STARTUP MOUNT - The database is mounted
STARTUP OPEN - The database is opened
16. What column differentiates the V$ views to the GV$ views and how?
The INST_ID column which indicates the instance in a RAC environment the information came from.
17. How would you go about generating an EXPLAIN plan?
Create a plan table with utlxplan.sql.
Use the explain plan set statement_id = 'tst1' into plan_table for a SQL statement
Look at the explain plan with utlxplp.sql or utlxpls.sql
18. How would you go about increasing the buffer cache hit ratio?
Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command.
19. Explain an ORA-01555
You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message.
20. Explain the difference between $ORACLE_HOME and $ORACLE_BASE.
ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.
21.  How would you determine the time zone under which a database was operating?
select DBTIMEZONE from dual;
22.  Explain the use of setting GLOBAL_NAMES equal to TRUE.
Setting GLOBAL_NAMES dictates how you might connect to a database. This variable is either TRUE or FALSE and if it is set to TRUE it enforces database links to have the same name as the remote database to which they are linking.
23.  What command would you use to encrypt a PL/SQL application?
WRAP
24.  Explain the difference between a FUNCTION, PROCEDURE and PACKAGE.
A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package on the other hand is a collection of functions and procedures that are grouped together based on their commonality to a business function or application.
25.  Explain the use of table functions.
Table functions are designed to return a set of rows through PL/SQL logic but are intended to be used as a normal table or view in a SQL statement. They are also used to pipeline information in an ETL process.
26.  Name three advisory statistics you can collect.
Buffer Cache Advice, Segment Level Statistics, & Timed Statistics
27.  Where in the Oracle directory tree structure are audit traces placed?
In unix $ORACLE_HOME/rdbms/audit, in Windows the event viewer
28.  Explain materialized views and how they are used.
Materialized views are objects that are reduced sets of information that have been summarized, grouped, or aggregated from base tables. They are typically used in data warehouse or decision support systems.
29.  When a user process fails, what background process cleans up after it?
PMON
30.  What background process refreshes materialized views?
The Job Queue Processes.
31.  How would you determine what sessions are connected and what resources they are waiting for?
Use of V$SESSION and V$SESSION_WAIT
32.  Describe what redo logs are.
Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database.
33.  How would you force a log switch?
ALTER SYSTEM SWITCH LOGFILE;
34.  Give two methods you could use to determine what DDL changes have been made.
You could use Logminer or Streams
35.  What does coalescing a tablespace do?
Coalescing is only valid for dictionary-managed tablespaces and de-fragments space by combining neighboring free extents into large single extents.
36.  What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace?
A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database.
37.  Name a tablespace automatically created when you create a database.
The SYSTEM tablespace.
38.  When creating a user, what permissions must you grant to allow them to connect to the database?
Grant the CONNECT to the user.
39.  How do you add a data file to a tablespace?
ALTER TABLESPACE <tablespace_name> ADD DATAFILE <datafile_name> SIZE <size>
40.  How do you resize a data file?
ALTER DATABASE DATAFILE <datafile_name> RESIZE <new_size>;
41.  What view would you use to look at the size of a data file?
DBA_DATA_FILES
42.  What view would you use to determine free space in a tablespace?
DBA_FREE_SPACE
43.  How would you determine who has added a row to a table?
Turn on fine grain auditing for the table.
44.  How can you rebuild an index?
ALTER INDEX <index_name> REBUILD;
45.  Explain what partitioning is and what its benefit is.
Partitioning is a method of taking large tables and indexes and splitting them into smaller, more manageable pieces.
46.  You have just compiled a PL/SQL package but got errors, how would you view the errors?
SHOW ERRORS
47.  How can you gather statistics on a table?
The ANALYZE command.
48.  How can you enable a trace for a session?
Use the DBMS_SESSION.SET_SQL_TRACE or
Use ALTER SESSION SET SQL_TRACE = TRUE;
49.  What is the difference between the SQL*Loader and IMPORT utilities?
These two Oracle utilities are used for loading data into the database. The difference is that the import utility relies on the data being produced by another Oracle utility EXPORT while the SQL*Loader utility allows data to be loaded that has been produced by other utilities from different data sources just so long as it conforms to ASCII formatted or delimited files.
50.  Name two files used for network connection to a database.
TNSNAMES.ORA and SQLNET.ORA
51. Ask 'How would you identify the bottlenecks in Database performance ?'
The answer is to examine the Oracle Execution Plan, and to make sure that the  appropriate Indexes exist and are used by the Oracle Optimizer.
52. Ask 'How do you find the numbert of rows in a Table ?'
A bad answer is count them (SELECT COUNT(*) FROM table_name)    A good answer is :-    'By generating SQL to ANALYZE TABLE table_name COUNT STATISTICS  by querying Oracle System Catalogues (e.g. USER_TABLES or ALL_TABLES). The best answer is to refer to the utility which Oracle released which makes it unnecessary to do ANALYZE TABLE for each Table individually.
53)How much database size does the Oracle recommend that one should have, and is this the default ?

Oracle DBA
1. SNAPSHOT is used for
[DBA] a] Synonym, b] Table space, c] System server, d] Dynamic data
replication Ans : D
2. We can create SNAPSHOTLOG for
[DBA] a] Simple snapshots, b] Complex snapshots, c] Both A & B, d]
Neither A nor B Ans : A
3. Transactions per rollback segment is derived from
[DBA] a] Db_Block_Buffers, b] Processes, c] Shared_Pool_Size, d] None
of the above Ans : B
4. ENQUEUE resources parameter information is derived from
[DBA] a] Processes or DDL_LOCKS and DML_LOCKS, b] LOG_BUFFER,
c] DB__BLOCK_SIZE.. Ans : A
5. LGWR process writes information into
a] Database files, b] Control files, c] Redolog files, d] All the
above. Ans : C
6. SET TRANSACTION USE ROLLBACK SEGMENT is used to create user
objects in a particular Tablespace
a] True, b] False Ans : False
7. Databases overall structure is maintained in a file called
a] Redolog file, b] Data file, c] Control file, d] All of the above. Ans : C
8. These following parameters are optional in init.ora parameter file DB_BLOCK_SIZE, PROCESSES a] True, b] False
Ans : False
9. Constraints cannot be exported through EXPORT command a] True, b] False
Ans : False
10. It is very difficult to grant and manage common privileges needed by different groups of database users using the roles a] True, b] False
Ans : False
33. What is a trigger
a] A piece of logic written in PL/SQL b] Executed at the arrival of a SQL*FORMS event c] Both A & B d] None of the above
Ans : C
34. Which of the folowing is TRUE for a ERASE packaged procedure
1] ERASE removes an indicated Global variable & releases the memory
associated with it 2] ERASE is used to remove a field from a page 1] Only 1 is TRUE 2] Only 2 is TRUE 3] Both 1 & 2 are TRUE 4] Both 1 & 2 are FALSE
Ans : 1
35. All datafiles related to a Tablespace are removed when the Tablespace is dropped
a] TRUE b] FALSE
Ans : B
36. Size of Tablespace can be increased by
a] Increasing the size of one of the Datafiles b] Adding one or more Datafiles c] Cannot be increased d] None of the above
Ans : B
37. Multiple Tablespaces can share a single datafile
a] TRUE b] FALSE
Ans : B
38. A set of Dictionary tables are created
a] Once for the Entire Database b] Every time a user is created c] Every time a Tablespace is created d] None of the above
Ans : A
39. Datadictionary can span across multiple Tablespaces a] TRUE b] FALSE
Ans : B
40. What is a DATABLOCK
a] Set of Extents b] Set of Segments c] Smallest Database storage unit d] None of the above
Ans : C
41. Can an Integrity Constraint be enforced on a table if some existing table data does not satisfy the constraint a] Yes b] No
Ans : B
42. A column defined as PRIMARY KEY can have NULL's a] TRUE b] FALSE
Ans : B
43. A Transaction ends a] Only when it is Committed b] Only when it is Rolledback c] When it is Committed or Rolledback d] None of the above
Ans : C
44. A Database Procedure is stored in the Database
a] In compiled form b] As source code c] Both A & B d] Not stored
Ans : C
45. A database trigger doesnot apply to data loaded before the definition of the trigger a] TRUE b] FALSE
Ans : A
46. Dedicated server configuration is
a] One server process - Many user processes b] Many server processes - One user process c] One server process - One user process d] Many server processes - Many user processes
Ans : C
47. Which of the following does not affect the size of the SGA
a] Database buffer b] Redolog buffer c] Stored procedure d] Shared pool
Ans : C
48. What does a COMMIT statement do to a CURSOR
a] Open the Cursor b] Fetch the Cursor c] Close the Cursor d] None of the above
Ans : D

49. Which of the following is TRUE
1] Host variables are declared anywhere in the program
2] Host variables are declared in the DECLARE section
a] Only 1 is TRUE b] Only 2 is TRUE c] Both 1 & 2are TRUE d] Both are FALSE
Ans : B
50. Which of the following is NOT VALID is PL/SQL
a] Bool boolean; b] NUM1, NUM2 number; c] deptname dept.dname%type; d] date1 date := sysdate
Ans : B
51. Declare  fvar number := null; svar number := 5 Begin goto << fproc>> if fvar is null then  << fproc>>
svar := svar + 5 end if; End; What will be the value of svar after the execution ?
a] Error b] 10 c] 5 d] None of the above
Ans : A
52. Which of the following is not correct about an Exception ?
a] Raised automatically / Explicitly in response to an ORACLE_ERROR b] An exception will be raised when an error occurs in that block c] Process terminates after completion of error sequence. d] A Procedure or Sequence of statements may be processed.
Ans : C
53. Which of the following is not correct about User_Defined Exceptions ?
a] Must be declared b] Must be raised explicitly c] Raised automatically in response to an Oracle error d] None of the above
Ans : C
54. A Stored Procedure is a
a] Sequence of SQL or PL/SQL statements to perform specific function  b] Stored in compiled form in the database c] Can be called from all client environments d] All of the above
Ans : D
55. Which of the following statement is false
a] Any procedure can raise an error and return an user message and error number b] Error number ranging from 20000 to 20999 are reserved for user defined messages c] Oracle checks Uniqueness of User defined errors d] Raise_Application_error is used for raising an user defined error.
Ans : C
56. Is it possible to open a cursor which is in a Package in another procedure ? a] Yes b] No
Ans : A
57. Is it possible to use Transactional control statements in Database Triggers ? a] Yes b] No
Ans : B
58. Is it possible to Enable or Disable a Database trigger ? a] Yes b] No
Ans : A
59. PL/SQL supports datatype(s)
a] Scalar datatype b] Composite datatype c] All of the above d] None of the above
Ans C
60. Find the ODD datatype out
a] VARCHAR2 b] RECORD c] BOOLEAN d] RAW
Ans : B
61. Which of the following is not correct about the "TABLE" datatype ?
a] Can contain any no of columns b] Simulates a One-dimensional array of unlimited size c] Column datatype of any Scalar type d] None of the above
Ans : A
62. Find the ODD one out of the following
a] OPEN b] CLOSE c] INSERT d] FETCH
Ans C
63. Which of the following is not correct about Cursor ?
a] Cursor is a named Private SQL area b] Cursor holds temporary results c] Cursor is used for retrieving multiple rows d] SQL uses implicit Cursors to retrieve rows
Ans : B
64. Which of the following is NOT VALID in PL/SQL ?
a] Select ... into b] Update c] Create d] Delete
Ans : C
65. What is the Result of the following 'VIK'||NULL||'RAM' ?
a] Error b] VIK RAM c] VIKRAM d] NULL
Ans : C
66. Declare a number := 5; b number := null; c number := 10; Begin if a > b AND a < c then a := c * a; end if; End; What will be the value of 'a' after execution ?
a] 50 b] NULL c] 5 d] None of the above
Ans : C
67. Does the Database trigger will fire when the table is TRUNCATED ? a] Yes b] No
Ans : B
68. SUBSTR(SQUARE ANS ALWAYS WORK HARD,14,6) will return a] ALWAYS b} S ALWA c] ALWAYS
Ans : C
69. REPLACE('JACK AND JUE','J','BL') will return
a] JACK AND BLUE b] BLACK AND JACK c] BLACK AND BLUE d] None of the above
Ans : C
70. TRANSLATE('333SQD234','0123456789ABCDPQRST','0123456789') will return
a] 333234 b] 333333  c] 234333 d] None of the above
Ans : A
71. EMPNO ENAME SAL A822 RAMASWAMY 3500 A812 NARAYAN 5000 A973 UMESH 2850 A500 BALAJI 5750 Use these data for the following Questions Select SAL from EMP E1 where 3 > ( Select count(*) from Emp E2 where E1.SAL > E2.SAL ) will retrieve
a] 3500,5000,2500 b] 5000,2850 c] 2850,5750 d] 5000,5750
Ans : A
72. Is it possible to modify a Datatype of a column when column contains data ? a] Yes b] No
Ans B
73. Which of the following is not correct about a View ?
a] To protect some of the columns of a table from other users b] Ocuupies data storage space c] To hide complexity of a query d] To hide complexity of a calculations
Ans : B
74. Which is not part of the Data Definiton Language ?  a] CREATE b] ALTER c] ALTER SESSION
Ans : C
75. The Data Manipulation Language statements are a] INSERT b] UPDATE c] SELECT d] All above
Ans : D
76. EMPNO ENAME SAL A822 RAMASWAMY 3500 A812 NARAYAN 5000 A973 UMESH A500 BALAJI 5750 Using the above data Select count(sal) from Emp will retrieve a] 1 b] 0 c] 3 d] None of the above
Ans : C
77. If an UNIQUE KEY constraint on DATE column is created, will it accept the rows that are inserted with SYSDATE ? a] Will b] Won't
Ans : B
78. What are the different events in Triggers ? a] Define, Create b] Drop, Comment c] Insert, Update, Delete d] All of the above
Ans : C

121. Sequence of events takes place while starting a Database is a] Database opened, File mounted, Instance started b] Instance started, Database mounted & Database opened c] Database opened, Instance started & file mounted d] Files mounted, Instance started & Database opened
Ans : B
122. SYSTEM TABLESPACE can be made off-line a] Yes b] No
Ans : B
123. ENQUEUE_RESOURCES parameter information is derived from
a] PROCESS or DDL_LOCKS & DML_LOCKS b] LOG BUFFER c] DB_BLOCK_SIZE d] DB_BLOCK_BUFFERS
Ans : A
124. SMON process is used to write into LOG files a] TRUE b] FALSE
Ans : B
125. EXP command is used  a] To take Backup of the Oracle Database b] To import data from the exported dump file c] To create Rollback segments d] None of the above
Ans : A
126. SNAPSHOTS cannot be refreshed automatically a] TRUE b] FALSE
Ans : B
127. The User can set Archive file name formats a] TRUE b] FALSE
Ans : A
128. The following parameters are optional in init.ora parameter file DB_BLOCK_SIZE, PROCESS a} TRUE b] FALSE
Ans : B
129. NOARCHIEVELOG parameter is used to enable the database in Archieve mode
a] TRUE b] FALSE
Ans : B
130. Constraints cannot be exported through Export command? a] TRUE b] FALSE
Ans : B
131. It is very difficult to grant and manage common priveleges needed by different groups of database users using roles a] TRUE b] FALSE
Ans : B
132. The status of the Rollback segment can be viewed through
a] DBA_SEGMENTS b] DBA_ROLES c] DBA_FREE_SPACES d] DBA_ROLLBACK_SEG
Ans : D
133. Explicitly we can assign transaction to a rollback segment a] TRUE B] FALSE
Ans : A
134. What file is read by ODBC to load drivers ?
a] ODBC.INI b] ODBC.DLL c] ODBCDRV.INI d] None of the above
Ans : A

RDBMS
1. What is database?
A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.
2. What is DBMS?
It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.
3. What is a Database system?
The database and DBMS software together is called as Database system.
4. Advantages of DBMS?
 Redundancy is controlled.  Unauthorised access is restricted. Providing multiple user interfaces.  Enforcing integrity constraints.  Providing backup and recovery.
5. Disadvantage in File Processing System?
 Data redundancy & inconsistency.  Difficult in accessing data.  Data isolation.  Data integrity.  Concurrent access is not possible.  Security Problems.
6. Describe the three levels of data abstraction?
The are three levels of abstraction:  Physical level: The lowest level of abstraction describes how data are stored.  Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.  View level: The highest level of abstraction describes only part of entire database.
7. Define the "integrity rules"
There are two Integrity rules. Entity Integrity: States that “Primary key cannot have NULL value” Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.
8. What is extension and intension?
Extension - It is the number of tuples present in a table at any instance. This is time dependent.
Intension - It is a constant value that gives the name, structure of table and the constraints laid on it.
9. What is System R? What are its two major subsystems?
System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system. Its two subsystems are. Research Storage. System Relational Data System.
10. How is the data structure of System R different from the relational structure?
Unlike Relational systems in System R.  Domains are not supported. Enforcement of candidate key uniqueness is optional. Enforcement of entity integrity is optional.  Referential integrity is not enforced
11. What is Data Independence?
Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level. Two types of Data Independence:
Physical Data Independence: Modification in physical level should not affect the logical level.
Logical Data Independence: Modification in logical level should affect the view level.  NOTE: Logical Data Independence is more difficult to achieve
12. What is a view? How it is related to data independence?
A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.
Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.
13. What is Data Model?
A collection of conceptual tools for describing data, data relationships data semantics and constraints.
14. What is E-R model?
This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
15. What is Object Oriented model?
This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
16. What is an Entity?
It is a 'thing' in the real world with an independent existence.
17. What is an Entity type?
It is a collection (set) of entities that have same attributes.
18. What is an Entity set?
It is a collection of all entities of particular entity type in the database.
19. What is an Extension of entity type?
The collections of entities of a particular entity type are grouped together into an entity set.
20. What is Weak Entity set?
An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.
21. What is an attribute?
It is a particular property, which describes the entity.
22. What is a Relation Schema and a Relation?
A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).
23. What is degree of a Relation?
It is the number of attribute of its relation schema.
24. What is Relationship?
It is an association among two or more entities.
25. What is Relationship set?
The collection (or set) of similar relationships.
26. What is Relationship type?
Relationship type defines a set of associations or a relationship set among a given set of entity types.
27. What is degree of Relationship type?
It is the number of entity type participating.
28. What is DDL (Data Definition Language)?
A data base schema is specifies by a set of definitions expressed by a special language called DDL.
29. What is VDL (View Definition Language)?
It specifies user views and their mappings to the conceptual schema.
30. What is SDL (Storage Definition Language)?
This language is to specify the internal schema. This language may specify the mapping between two schemas.
31. What is Data Storage - Definition Language?
The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.
32. What is DML (Data Manipulation Language)?
This language that enable user to access or manipulate data as organised by appropriate data model.  Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data. Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.
33. What is DML Compiler?
It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
34. What is Query evaluation engine?
It executes low-level instruction generated by compiler.
35. What is DDL Interpreter?
It interprets DDL statements and record them in tables containing metadata.
36. What is Record-at-a-time?
The Low level or Procedural DML can specify and retrieve each record from a set of records. This retrieve of a record is said to be Record-at-a-time.
37. What is Set-at-a-time or Set-oriented?
The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.
38. What is Relational Algebra?
It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.
39. What is Relational Calculus?
It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.

40. How does Tuple-oriented relational calculus differ from domain-oriented relational calculus
The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL The domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.
41. What is normalization?
It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties   Minimizing redundancy. Minimizing insertion, deletion and update anomalies.
42. What is Functional Dependency?
A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.
43. When is a functional dependency F said to be minimal?
 Every dependency in F has a single attribute for its right hand side. We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F. We cannot remove any dependency from F and still have set of dependency that is equivalent to F.
44. What is Multivalued dependency?
Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
t3[x] = t4[X] = t1[X] = t2[X]. 
t3[Y] = t1[Y] and t4[Y] = t2[Y].
t3[Z] = t2[Z] and t4[Z] = t1[Z].
where [Z = (R-(X U Y)) ].
45. What is Lossless join property?
It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.
46. What is 1 NF (Normal Form)?
The domain of attribute must include only atomic (simple, indivisible) values.
47. What is Fully Functional dependency?
It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
48. What is 2NF?
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
49. What is 3NF?
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true. X is a Super-key of R. A is a prime attribute of R. In other words, if every non prime attribute is non-transitively dependent on primary key.
50. What is BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key. 
51. What is 4NF?
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true. X is subset or equal to (or) XY = R.    X is a super key.
52. What is 5NF?
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true.  Ri = R for some i.    The join dependency is implied by the set of FD, over R in which the left side is key of R.
53. What is Domain-Key Normal Form?
A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.
54. What are partial, alternate,, artificial, compound and natural key?
Partial Key:  It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.  Alternate Key:  All Candidate Keys excluding the Primary Key are known as Alternate Keys.  Artificial Key:  If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.  Compound Key:  If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key. Natural Key:  When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key.
55. What is indexing and what are the different kinds of indexing?
Indexing is a technique for determining how quickly specific data can be found.
Types:
Binary search style indexing.   B-Tree indexing.  Inverted list indexing.   Memory resident table.   Table indexing.
56. What is system catalog or catalog relation? How is better known as?
A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.
57. What is meant by query optimization?
The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.
58. What is join dependency and inclusion dependency?
Join Dependency:  A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.  Inclusion Dependency:  An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.
59. What is durability in DBMS?
Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.
60. What do you mean by atomicity and aggregation?
Atomicity:  Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.  Aggregation: A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.
61. What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.
62. What is a checkpoint and When does it occur?
A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.
63. What are the different phases of transaction?
Different phases are.  Analysis phase.  Redo Phase.  Undo phase.
64. What do you mean by flat file database?
It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management. 
65. What is "transparent DBMS"?
It is one, which keeps its Physical Structure hidden from user.
66. Brief theory of Network, Hierarchical schemas and their properties
Network schema uses a graph data structure to organize records example for such a database management system is CTCG while a hierarchical schema uses a tree data structure example for such a system is IMS.
67. What is a query?
A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.
68. What do you mean by Correlated subquery?
Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery. A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery. E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)
69. What are the primitive operations common to all record management systems?
Addition, deletion and modification.
70. Name the buffer in which all the commands that are typed in are stored
‘Edit’ Buffer
71. What are the unary operations in Relational Algebra?
PROJECTION and SELECTION.
72. Are the resulting relations of PRODUCT and JOIN operation the same?
No.  PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.
73. What is RDBMS KERNEL?
Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database  You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures
74. Name the sub-systems of a RDBMS
I/O, Security, Language Processing, Process Control, Storage Management, Logging and Recovery, Distribution Control, Transaction Control, Memory Management, Lock Management
75. Which part of the RDBMS takes care of the data dictionary? How
Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.
76. What is the job of the information stored in data-dictionary?
The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.
77. Not only RDBMS takes care of locating data it also
determines an optimal access path to store or retrieve the data
76. How do you communicate with an RDBMS?
You communicate with an RDBMS using Structured Query Language (SQL)
78. Define SQL and state the differences between SQL and other conventional programming Languages
SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.
79. Name the three major set of files on disk that compose a database in Oracle
There are three major sets of files on disk that compose a database. All the files are binary. These are  Database files.  Control files.  Redo logs. The most important of these are the database files where the actual data resides. The control files and the redo logs support the functioning of the architecture itself. All three sets of files must be present, open, and available to Oracle for any data on the database to be useable. Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one.
80. What is an Oracle Instance?
The Oracle system processes, also known as Oracle background processes, provide functions for the user processes—functions that would otherwise be done by the user processes themselves
Oracle database-wide system memory is known as the SGA, the system global area or shared global area. The data and control structures in the SGA are shareable, and all the Oracle background processes and user processes can use them. The combination of the SGA and the Oracle background processes is known as an Oracle instance
81. What are the four Oracle system processes that must always be up and running for the database to be useable
The four Oracle system processes that must always be up and running for the database to be useable include DBWR (Database Writer), LGWR (Log Writer), SMON (System Monitor), and PMON (Process Monitor).
82. What are database files, control files and log files. How many of these files should a database have at least? Why?
Database Files. The database files hold the actual data and are typically the largest in size. Depending on their sizes, the tables (and other objects) for all the user accounts can go in one database file—but that's not an ideal situation because it does not make the database structure very flexible for controlling access to storage for different users, putting the database on different disk drives, or backing up and restoring just part of the database.
You must have at least one database file but usually, more than one files are used. In terms of accessing and using the data in the tables and other objects, the number (or location) of the files is immaterial.  The database files are fixed in size and never grow bigger than the size at which they were created. Control Files :The control files and redo logs support the rest of the architecture. Any database must have at least one control file, although you typically have more than one to guard against loss. The control file records the name of the database, the date and time it was created, the location of the database and redo logs, and the synchronization information to ensure that all three sets of files are always in step. Every time you add a new database or redo log file to the database, the information is recorded in the control files.
Redo Logs: Any database must have at least two redo logs. These are the journals for the database; the redo logs record all changes to the user objects or system objects. If any type of failure occurs, the changes recorded in the redo logs can be used to bring the database to a consistent state without losing any committed transactions. In the case of non-data loss failure, Oracle can apply the information in the redo logs automatically without intervention from the DBA. The redo log files are fixed in size and never grow dynamically from the size at which they were created.
83. What is ROWID?
The ROWID is a unique database-wide physical address for every row on every table. Once assigned (when the row is first inserted into the database), it never changes until the row is deleted or the table is dropped. The ROWID consists of the following three components, the combination of which uniquely identifies the physical storage location of the row. Oracle database file number, which contains the block with the rows.  Oracle block address, which contains the row
The row within the block (because each block can hold many rows). The ROWID is used internally in indexes as a quick means of retrieving rows with a particular key value. Application developers also use it in SQL statements as a quick way to access a row once they know the ROWID
84. What is Oracle Block? Can two Oracle Blocks have the same address?
Oracle "formats" the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.
85. What is database Trigger?
A database trigger is a PL/SQL block that can defined to automatically execute for insert, update, and delete statements against a table. The trigger can e defined to execute once for the entire statement or once for every row that is inserted, updated, or deleted. For any one table, there are twelve events for which you can define database triggers. A database trigger can call database procedures that are also written in PL/SQL.
86. Name two utilities that Oracle provides, which are use for backup and recovery.
Along with the RDBMS software, Oracle provides two utilities that you can use to back up and restore the database. These utilities are Export and Import. The Export utility dumps the definitions and data for the specified part of the database to an operating system binary file. The Import utility reads the file produced by an export, recreates the definitions of objects, and inserts the data  If Export and Import are used as a means of backing up and recovering the database, all the changes made to the database cannot be recovered since the export was performed. The best you can do is recover the database to the time when the export was last performed.
87. What are stored-procedures? And what are the advantages of using them.
Stored procedures are database objects that perform a user defined operation. A stored procedure can have a set of compound SQL statements. A stored procedure executes the SQL commands and returns the result to the client. Stored procedures are used to reduce network traffic.
88. How are exceptions handled in PL/SQL? Give some of the internal exceptions' name
PL/SQL exception handling is a mechanism for dealing with run-time errors encountered during procedure execution. Use of this mechanism enables execution to continue if the error is not severe enough to cause procedure termination.  The exception handler must be defined within a subprogram specification. Errors cause the program to raise an exception with a transfer of control to the exception-handler block. After the exception handler executes, control returns to the block in which the handler was defined. If there are no more executable statements in the block, control returns to the caller. User-Defined Exceptions: PL/SQL enables the user to define exception handlers in the declarations area of subprogram specifications. User accomplishes this by naming an exception as in the following example: ot_failure EXCEPTION;
In this case, the exception name is ot_failure. Code associated with this handler is written in the EXCEPTION specification area as follows:  EXCEPTION  when OT_FAILURE then out_status_code := g_out_status_code; out_msg := g_out_msg; The following is an example of a subprogram exception:
EXCEPTION  when NO_DATA_FOUND then g_out_status_code := 'FAIL'; RAISE ot_failure;  Within this exception is the RAISE statement that transfers control back to the ot_failure exception handler. This technique of raising the exception is used to invoke all user-defined exceptions.
System-Defined Exceptions:  Exceptions internal to PL/SQL are raised automatically upon error. NO_DATA_FOUND is a system-defined exception. Table below gives a complete list of internal exceptions.
PL/SQL internal exceptions. Exception Name Oracle Error
CURSOR_ALREADY_OPEN ORA-06511 DUP_VAL_ON_INDEX ORA-00001  INVALID_CURSOR ORA-01001 INVALID_NUMBER ORA-01722 LOGIN_DENIED ORA-01017 NO_DATA_FOUND ORA-01403 NOT_LOGGED_ON ORA-01012 PROGRAM_ERROR ORA-06501 STORAGE_ERROR ORA-06500 TIMEOUT_ON_RESOURCE ORA-00051 TOO_MANY_ROWS ORA-01422 TRANSACTION_BACKED_OUT ORA-00061 VALUE_ERROR ORA-06502 ZERO_DIVIDE ORA-01476
In addition to this list of exceptions, there is a catch-all exception named OTHERS that traps all errors for which specific error handling has not been established.
89. Does PL/SQL support "overloading"? Explain
The concept of overloading in PL/SQL relates to the idea that you can define procedures and functions with the same name. PL/SQL does not look only at the referenced name, however, to resolve a procedure or function call. The count and data types of formal parameters are also considered.  PL/SQL also attempts to resolve any procedure or function calls in locally defined packages before looking at globally defined packages or internal functions. To further ensure calling the proper procedure, you can use the dot notation. Prefacing a procedure or function name with the package name fully qualifies any procedure or function reference.
90. Tables derived from the ERD
a) Are totally unnormalised b) Are always in 1NF c) Can be further denormalised d) May have multi-valued attributes
(b) Are always in 1NF
91. Spurious tuples may occur due to
i. Bad normalization ii. Theta joins iii. Updating tables from join
a) i & ii b) ii & iii c) i & iii d) ii & iii
(a) i & iii because theta joins are joins made on keys that are not primary keys.
92. A B C is a set of attributes. The functional dependency is as follows
AB -> B  AC -> C  C -> B
a) is in 1NF b) is in 2NF c) is in 3NF d) is in BCNF
(a) is in 1NF since (AC)+ = { A, B, C} hence AC is the primary key. Since C B is a FD given, where neither C is a Key nor B is a prime attribute, this it is not in 3NF. Further B is not functionally dependent on key AC thus it is not in 2NF. Thus the given FDs is in 1NF.
93. In mapping of ERD to DFD
a) entities in ERD should correspond to an existing entity/store in DFD  b) entity in DFD is converted to attributes of an entity in ERD c) relations in ERD has 1 to 1 correspondence to processes in DFD d) relationships in ERD has 1 to 1 correspondence to flows in DFD
(a) entities in ERD should correspond to an existing entity/store in DFD
94. A dominant entity is the entity
a) on the N side in a 1 : N relationship  b) on the 1 side in a 1 : N relationship c) on either side in a 1 : 1 relationship  d) nothing to do with 1 : 1 or 1 : N relationship
(b) on the 1 side in a 1 : N relationship
95. Select 'NORTH', CUSTOMER From CUST_DTLS Where REGION = 'N' Order By
CUSTOMER Union Select 'EAST', CUSTOMER From CUST_DTLS Where REGION = 'E' Order By CUSTOMER  The above is
a) Not an error  b) Error - the string in single quotes 'NORTH' and 'SOUTH'  c) Error - the string should be in double quotes  d) Error - ORDER BY clause
(d) Error - the ORDER BY clause. Since ORDER BY clause cannot be used in UNIONS
96. What is Storage Manager?
It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.

97. What is Buffer Manager?
It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory.
98. What is Transaction Manager?
It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.
99. What is File Manager?
It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.
100. What is Authorization and Integrity manager?
It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data.
101. What are stand-alone procedures?
Procedures that are not part of a package are known as stand-alone because they independently defined. A good example of a stand-alone procedure is one written in a SQL*Forms application. These types of procedures are not available for reference from other Oracle tools. Another limitation of stand-alone procedures is that they are compiled at run time, which slows execution.
102. What are cursors give different types of cursors.
PL/SQL uses cursors for all database information accesses statements. The language supports the use two types of cursors.  Implicit.  Explicit.
103. What is cold backup and hot backup (in case of Oracle)?
Cold Backup: It is copying the three sets of files (database files, redo logs, and control file) when the instance is shut down. This is a straight file copy, usually from the disk directly to tape. You must shut down the instance to guarantee a consistent copy. If a cold backup is performed, the only option available in the event of data file loss is restoring all the files from the latest backup. All work performed on the database since the last backup is lost.  Hot Backup:  Some sites (such as worldwide airline reservations systems) cannot shut down the database while making a backup copy of the files. The cold backup is not an available option. So different means of backing up database must be used — the hot backup. Issue a SQL command to indicate to Oracle, on a tablespace-by-tablespace basis, that the files of the tablespace are to backed up. The users can continue to make full use of the files, including making changes to the data. Once the user has indicated that he/she wants to back up the tablespace files, he/she can use the operating system to copy those files to the desired backup destination. The database must be running in ARCHIVELOG mode for the hot backup option. If a data loss failure does occur, the lost database files can be restored using the hot backup and the online and offline redo logs created since the backup was done. The database is restored to the most consistent state without any loss of committed transactions.
104. What are Armstrong rules? How do we say that they are complete and/or sound
The well-known inference rules for FDs.   Reflexive rule : If Y is subset or equal to X then X Y.   Augmentation rule:  If X Y then XZ YZ.  Transitive rule:  If {X Y, Y Z} then X Z.  Decomposition rule : If X YZ then X Y.   Union or Additive rule:  If {X Y, X Z} then X YZ.  Pseudo Transitive rule :  If {X Y, WY Z} then WX Z.  Of these the first three are known as Amstrong Rules. They are sound because it is enough if a set of FDs satisfy these three. They are called complete because using these three rules we can generate the rest all inference rules.
105. How can you find the minimal key of relational schema?
Minimal key is one which can identify each tuple of the given relation schema uniquely. For finding the minimal key it is required to find the closure that is the set of all attributes that are dependent on any given set of attributes under the given set of functional dependency.
Algo. I Determining X+, closure for X, given set of FDs F  1. Set X+ = X  2. Set Old X+ = X+  3. For each FD Y Z in F and if Y belongs to X+ then add Z to X+  4. Repeat steps 2 and 3 until Old X+ = X+  Algo.II Determining minimal K for relation schema R, given set of FDs F  1. Set K to R that is make K a set of all attributes in R  2. For each attribute A in K  a. Compute (K – A)+ with respect to F  b. If (K – A)+ = R then set K = (K – A)+
106. What do you understand by dependency preservation?
Given a relation R and a set of FDs F, dependency preservation states that the closure of the union of the projection of F on each decomposed relation Ri is equal to the closure of F. i.e.,
((PR1(F)) U … U (PRn(F)))+ = F+ if decomposition is not dependency preserving, then some dependency is lost in the decomposition.










107. What is meant by Proactive, Retroactive and Simultaneous Update.
Proactive Update: The updates that are applied to database before it becomes effective in real world . Retroactive Update:  The updates that are applied to database after it becomes effective in real world .  Simulatneous Update:  The updates that are applied to database at the same time when it becomes effective in real world .
108. What are the different types of JOIN operations?
Equi Join: This is the most common type of join which involves only equality comparisions. The disadvantage in this type of join is that there SQL
1.Which is the subset of SQL commands used to manipulate Oracle Database structures, including tables?
Data Definition Language (DDL)
2. What operator performs pattern matching?
LIKE operator
3. What operator tests column for the absence of data?
IS NULL operator
4. Which command executes the contents of a specified file?
START <filename> or @<filename>
5. What is the parameter substitution symbol used with INSERT INTO command?
&
6. Which command displays the SQL command in the SQL buffer, and then executes it?  RUN
7. What are the wildcards used for pattern matching?
for single character substitution and % for multi-character substitution
8. State true or false. EXISTS, SOME, ANY are operators in SQL.
True
9. State true or false. !=, <>, ^= all denote the same operation.
True
10. What are the privileges that can be granted on a table by a user to others?
Insert, update, delete, select, references, index, execute, alter, all
11. What command is used to get back the privileges offered by the GRANT command? REVOKE
12. Which system tables contain information on privileges granted and privileges obtained? USER_TAB_PRIVS_MADE, USER_TAB_PRIVS_RECD
13. Which system table contains information on constraints on all the tables created?
USER_CONSTRAINTS
14. TRUNCATE TABLE EMP; DELETE FROM EMP;  Will the outputs of the above two commands differ? Both will result in deleting all the rows in the table EMP.
15. What is the difference between TRUNCATE and DELETE commands?
TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back. WHERE clause can be used with DELETE and not with TRUNCATE.

16. What command is used to create a table by copying the structure of another table?
Answer : CREATE TABLE .. AS SELECT command Explanation :To copy only the structure, the WHERE clause of the SELECT command should contain a FALSE statement as in the following. CREATE TABLE NEWTABLE AS SELECT * FROM EXISTINGTABLE WHERE 1=2; If the WHERE condition is true, then all the rows or rows satisfying the condition will be copied to the new table.
17. What will be the output of the following query?
SELECT REPLACE(TRANSLATE(LTRIM(RTRIM('!! ATHEN !!','!'), '!'), 'AN', '**'),'*','TROUBLE') FROM DUAL;
TROUBLETHETROUBLE
18. What will be the output of the following query?
SELECT DECODE(TRANSLATE('A','1234567890','1111111111'), '1','YES', 'NO' ); Answer : NO Explanation :
The query checks whether a given string is a numerical digit.
19. What does the following query do?
SELECT SAL + NVL(COMM,0) FROM EMP; This displays the total salary of all employees. The null values in the commission column will be replaced by 0 and added to salary.
20. Which date function is used to find the difference between two dates?
MONTHS_BETWEEN
21. Why does the following command give a compilation error?
DROP TABLE &TABLE_NAME;
Variable names should start with an alphabet. Here the table name starts with an '&' symbol.
22. What is the advantage of specifying WITH GRANT OPTION in the GRANT command?
The privilege receiver can further grant the privileges he/she has obtained from the owner to any other user.
23. What is the use of the DROP option in the ALTER TABLE command?
It is used to drop constraints specified on the table.
24. What is the value of ‘comm’ and ‘sal’ after executing the following query if the initial value of ‘sal’ is 10000?
UPDATE EMP SET SAL = SAL + 1000, COMM = SAL*0.1; sal = 11000, comm = 1000
25. What is the use of DESC in SQL?
Answer : DESC has two purposes. It is used to describe a schema as well as to retrieve rows from table in descending order.  Explanation : The query SELECT * FROM EMP ORDER BY ENAME DESC will display the output sorted on ENAME in descending order.
26. What is the use of CASCADE CONSTRAINTS?
When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.
27. Which function is used to find the largest integer less than or equal to a specific value?
FLOOR
28. What is the output of the following query?
SELECT TRUNC(1234.5678,-2) FROM DUAL; 1200

SQL – QUERIES
I. SCHEMAS Table 1 : STUDIES  PNAME (VARCHAR), SPLACE (VARCHAR), COURSE (VARCHAR), CCOST (NUMBER) Table 2 : SOFTWARE  PNAME (VARCHAR), TITLE (VARCHAR), DEVIN (VARCHAR), SCOST (NUMBER), DCOST (NUMBER), SOLD (NUMBER) Table 3 : PROGRAMMER  PNAME (VARCHAR), DOB (DATE), DOJ (DATE), SEX (CHAR), PROF1 (VARCHAR), PROF2 (VARCHAR), SAL (NUMBER) LEGEND : PNAME – Programmer Name, SPLACE – Study Place, CCOST – Course Cost, DEVIN – Developed in, SCOST – Software Cost, DCOST – Development Cost, PROF1 – Proficiency 1
QUERIES :
1. Find out the selling cost average for packages developed in Oracle.
2. Display the names, ages and experience of all programmers.
3. Display the names of those who have done the PGDCA course.
4. What is the highest number of copies sold by a package?
5. Display the names and date of birth of all programmers born in April.
6. Display the lowest course fee.
7. How many programmers have done the DCA course.
8. How much revenue has been earned through the sale of packages developed in C.
9. Display the details of software developed by Rakesh.
10. How many programmers studied at Pentafour.
11. Display the details of packages whose sales crossed the 5000 mark.
12. Find out the number of copies which should be sold in order to recover the development cost of each package.
13. Display the details of packages for which the development cost has been recovered.
14. What is the price of costliest software developed in VB?
15. How many packages were developed in Oracle ?
16. How many programmers studied at PRAGATHI?
17. How many programmers paid 10000 to 15000 for the course?
18. What is the average course fee?
19. Display the details of programmers knowing C.
20. How many programmers know either C or Pascal?
21. How many programmers don’t know C and C++?
22. How old is the oldest male programmer?
23. What is the average age of female programmers?
24. Calculate the experience in years for each programmer and display along with their names in descending order.
25. Who are the programmers who celebrate their birthdays during the current month?
26. How many female programmers are there?
27. What are the languages known by the male programmers?
28. What is the average salary?
29. How many people draw 5000 to 7500?
30. Display the details of those who don’t know C, C++ or Pascal.
31. Display the costliest package developed by each programmer.
32. Produce the following output for all the male programmers
KEYS:
1. SELECT AVG(SCOST) FROM SOFTWARE WHERE DEVIN = 'ORACLE';
2. SELECT PNAME,TRUNC(MONTHS_BETWEEN(SYSDATE,DOB)/12) "AGE", TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) "EXPERIENCE" FROM PROGRAMMER;
3. SELECT PNAME FROM STUDIES WHERE COURSE = 'PGDCA';
4. SELECT MAX(SOLD) FROM SOFTWARE;
5. SELECT PNAME, DOB FROM PROGRAMMER WHERE DOB LIKE '%APR%';
6. SELECT MIN(CCOST) FROM STUDIES;
7. SELECT COUNT(*) FROM STUDIES WHERE COURSE = 'DCA';
8. SELECT SUM(SCOST*SOLD-DCOST) FROM SOFTWARE GROUP BY DEVIN HAVING DEVIN = 'C';
9. SELECT * FROM SOFTWARE WHERE PNAME = 'RAKESH';
10. SELECT * FROM STUDIES WHERE SPLACE = 'PENTAFOUR';
11. SELECT * FROM SOFTWARE WHERE SCOST*SOLD-DCOST > 5000;
12. SELECT CEIL(DCOST/SCOST) FROM SOFTWARE;
13. SELECT * FROM SOFTWARE WHERE SCOST*SOLD >= DCOST;
14. SELECT MAX(SCOST) FROM SOFTWARE GROUP BY DEVIN HAVING DEVIN = 'VB';
15. SELECT COUNT(*) FROM SOFTWARE WHERE DEVIN = 'ORACLE';
16. SELECT COUNT(*) FROM STUDIES WHERE SPLACE = 'PRAGATHI';
17. SELECT COUNT(*) FROM STUDIES WHERE CCOST BETWEEN 10000 AND 15000;
18. SELECT AVG(CCOST) FROM STUDIES;
19. SELECT * FROM PROGRAMMER WHERE PROF1 = 'C' OR PROF2 = 'C';
20. SELECT * FROM PROGRAMMER WHERE PROF1 IN ('C','PASCAL') OR PROF2 IN ('C','PASCAL');
21. SELECT * FROM PROGRAMMER WHERE PROF1 NOT IN ('C','C++') AND PROF2 NOT IN ('C','C++');
22. SELECT TRUNC(MAX(MONTHS_BETWEEN(SYSDATE,DOB)/12)) FROM PROGRAMMER WHERE SEX = 'M';
23. SELECT TRUNC(AVG(MONTHS_BETWEEN(SYSDATE,DOB)/12)) FROM PROGRAMMER WHERE SEX = 'F';
24. SELECT PNAME, TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) FROM PROGRAMMER ORDER BY PNAME DESC;
25. SELECT PNAME FROM PROGRAMMER WHERE TO_CHAR(DOB,'MON') = TO_CHAR(SYSDATE,'MON');
26. SELECT COUNT(*) FROM PROGRAMMER WHERE SEX = 'F';
27. SELECT DISTINCT(PROF1) FROM PROGRAMMER WHERE SEX = 'M';
28. SELECT AVG(SAL) FROM PROGRAMMER;
29. SELECT COUNT(*) FROM PROGRAMMER WHERE SAL BETWEEN 5000 AND 7500;
30. SELECT * FROM PROGRAMMER WHERE PROF1 NOT IN ('C','C++','PASCAL') AND PROF2 NOT IN ('C','C++','PASCAL');
31. SELECT PNAME,TITLE,SCOST FROM SOFTWARE WHERE SCOST IN (SELECT MAX(SCOST) FROM SOFTWARE GROUP BY PNAME);
32.SELECT 'Mr.' || PNAME || ' - has ' || TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) || ' years of experience' “Programmer” FROM PROGRAMMER WHERE SEX = 'M' UNION SELECT 'Ms.' || PNAME || ' - has ' || TRUNC (MONTHS_BETWEEN (SYSDATE,DOJ)/12) || ' years of experience' “Programmer” FROM PROGRAMMER WHERE SEX = 'F';
II . SCHEMA :

Table 1 : DEPT

DEPTNO (NOT NULL , NUMBER(2)), DNAME (VARCHAR2(14)),
LOC (VARCHAR2(13)

Table 2 : EMP

EMPNO (NOT NULL , NUMBER(4)), ENAME (VARCHAR2(10)),
JOB (VARCHAR2(9)), MGR (NUMBER(4)), HIREDATE (DATE),
SAL (NUMBER(7,2)), COMM (NUMBER(7,2)), DEPTNO (NUMBER(2))

MGR is the empno of the employee whom the employee reports to. DEPTNO is a foreign key.
QUERIES
1. List all the employees who have at least one person reporting to them.
2. List the employee details if and only if more than 10 employees are present in department no 10.
3. List the name of the employees with their immediate higher authority.
4. List all the employees who do not manage any one.
5. List the employee details whose salary is greater than the lowest salary of an employee belonging to deptno 20.
6. List the details of the employee earning more than the highest paid manager.
7. List the highest salary paid for each job.
8. Find the most recently hired employee in each department.
9. In which year did most people join the company? Display the year and the number of employees.
10. Which department has the highest annual remuneration bill?
11. Write a query to display a ‘*’ against the row of the most recently hired employee.
12. Write a correlated sub-query to list out the employees who earn more than the average salary of their department.
13. Find the nth maximum salary.
14. Select the duplicate records (Records, which are inserted, that already exist) in the EMP table.
15. Write a query to list the length of service of the employees (of the form n years and m months).

KEYS:

1. SELECT DISTINCT(A.ENAME) FROM EMP A, EMP B WHERE A.EMPNO = B.MGR; or SELECT ENAME FROM EMP WHERE EMPNO IN (SELECT MGR FROM EMP);
2. SELECT * FROM EMP WHERE DEPTNO IN (SELECT DEPTNO FROM EMP GROUP BY DEPTNO HAVING COUNT(EMPNO)>10 AND DEPTNO=10);
3. SELECT A.ENAME "EMPLOYEE", B.ENAME "REPORTS TO" FROM EMP A, EMP B WHERE A.MGR=B.EMPNO;
4. SELECT * FROM EMP WHERE EMPNO IN ( SELECT EMPNO FROM EMP MINUS SELECT MGR FROM EMP);
5. SELECT * FROM EMP WHERE SAL > ( SELECT MIN(SAL) FROM EMP GROUP BY DEPTNO HAVING DEPTNO=20);
6. SELECT * FROM EMP WHERE SAL > ( SELECT MAX(SAL) FROM EMP GROUP BY JOB HAVING JOB = 'MANAGER' );
7. SELECT JOB, MAX(SAL) FROM EMP GROUP BY JOB;
8. SELECT * FROM EMP WHERE (DEPTNO, HIREDATE) IN (SELECT DEPTNO, MAX(HIREDATE) FROM EMP GROUP BY DEPTNO);
9. SELECT TO_CHAR(HIREDATE,'YYYY') "YEAR", COUNT(EMPNO) "NO. OF EMPLOYEES" FROM EMP GROUP BY TO_CHAR(HIREDATE,'YYYY') HAVING COUNT(EMPNO) = (SELECT MAX(COUNT(EMPNO)) FROM EMP GROUP BY TO_CHAR(HIREDATE,'YYYY'));
10. SELECT DEPTNO, LPAD(SUM(12*(SAL+NVL(COMM,0))),15) "COMPENSATION" FROM EMP GROUP BY DEPTNO HAVING SUM( 12*(SAL+NVL(COMM,0))) = (SELECT MAX(SUM(12*(SAL+NVL(COMM,0)))) FROM EMP GROUP BY DEPTNO);
11. SELECT ENAME, HIREDATE, LPAD('*', "RECENTLY HIRED" FROM EMP WHERE HIREDATE = (SELECT MAX(HIREDATE) FROM EMP) UNION SELECT ENAME NAME, HIREDATE, LPAD(' ',15) "RECENTLY HIRED" FROM EMP WHERE HIREDATE != (SELECT MAX(HIREDATE) FROM EMP);
12. SELECT ENAME,SAL FROM EMP E WHERE SAL > (SELECT AVG(SAL) FROM EMP F WHERE E.DEPTNO = F.DEPTNO);
13. SELECT ENAME, SAL FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT(SAL)) FROM EMP B WHERE A.SAL<=B.SAL);
14. SELECT * FROM EMP A WHERE A.EMPNO IN (SELECT EMPNO FROM EMP GROUP BY EMPNO HAVING COUNT(EMPNO)>1) AND A.ROWID!=MIN (ROWID));
15. SELECT ENAME "EMPLOYEE",TO_CHAR(TRUNC(MONTHS_BETWEEN(SYSDATE,HIREDATE)/12))||' YEARS '|| TO_CHAR(TRUNC(MOD(MONTHS_BETWEEN (SYSDATE, HIREDATE),12)))||' MONTHS ' “LENGTH OF SERVICE" FROM EMP;
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