Database [3i Infotech Placement]: Sample Questions 228 - 229 of 294

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Question 228

Database
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Statement

True-False▾

SET TRANSACTION USE ROLLBACK SEGMENT is used to create user objects in a particular Table space.

Answer

FALSE

Explanation

Transaction and Rollback Segments
  • The SET TRANSACTION statement:
    • Sets a transaction as read-only
    • Sets a transaction as read/write
    • Assigns a name to a transaction
    • Assigns a rollback segment to a transaction
  • The operation performed affects only our current transaction.
  • Transaction ends COMMIT or ROLLBACK statement is issued.
  • Oracle Database implicitly commits the current transaction before and after executing a data definition language statement.

Syntax of Set Transaction

SET TRANSACTION [READ ONLY|READ WRITE]

[ISOLATION LEVEL [SERIALIZE|READ COMMITED]

[USE ROLLBACK SEGMENT ‘segment_name’ ]

[Name ‘transaction_name’ ] ;

Question 229

Database
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Describe in Detail

Essay▾

What is Relational Algebra?

Explanation

Structure of Relational Algebra in DBMS
  • The relational algebra is a theoretical procedural query language which takes instance of relations and does operations that work on one or more relations to describe another relation without altering the original relation.
  • So, both the operands and the outputs are relations, and so the output from one operation can turn into the input to another operation which allows expressions to be nested in the relational algebra.
  • The relational algebra is a relation-at-a-time (or set) language where all tuples are controlled in one statement without the use of loop.
  • There are several variations of syntax for relational algebra commands and you use a common symbolic notation for the commands and present it informally.
  • The primary operations of relational algebra are as follows:
    • Select
    • Project
    • Union
    • Set different
    • Cartesian product
    • Rename

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