Oracle Data Base Interview Questions Part-2

What is a Sequence ?

A sequence generates a serial list of unique numbers for numerical columns of a database’s tables.

What is a Synonym ?

A synonym is an alias for a table, view, sequence or program unit.

What are the type of Synonyms?

There are two types of Synonyms Private and Public.

What is a Private Synonyms ?

A Private Synonyms can be accessed only by the owner.

What is a Public Synonyms ?

A Public synonyms can be accessed by any user on the database.

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.

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.

How are Indexes Update ?

Indexes are automatically maintained and used by ORACLE. Changes to table data are automatically incorporated into all relevant indexes.

What are Clusters?

Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

What is cluster Key?

The related columns of the tables in a cluster are called the Cluster Key.

What is Index Cluster ?

A Cluster with an index on the Cluster Key.

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.

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.

What is Database Link ?

A database link is a named object that describes a “path” from one database to another.

What are the types of Database Links ?

Private Database Link, Public Database Link & Network Database Link.

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.

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.

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.

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.

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 can’t be changed latter.

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.

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.

What is a Segment ?

A segment is a set of extents allocated for a certain logical structure.

What are the different type of Segments ?

Data Segment, Index Segment, Rollback Segment and Temporary Segment.

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.

What is an Index Segment ?

Each Index has an Index segment that stores all of its data.

What is Rollback Segment ?

A Database contains one or more Rollback Segments to temporarily store “undo” information.

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.

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.

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.

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 table space.

What is a Redo Log?

The set of Redo Log files for a database is collectively known as the database’s redo log.