Relational Algebra

Question 1

SELECT

Answer 1

The SELECT operation is used for selecting a subset of the tuples according to a given selection condition. Sigma(σ) Symbol denotes it. It is used as an expression to choose tuples which meet the selection condition. Select operator selects tuples that satisfy a given predicate.

Question 2

Projection

Answer 2

The projection eliminates all attributes of the input relation but those mentioned in the projection list. The projection method defines a relation that contains a vertical subset of Relation.

This helps to extract the values of specified attributes to eliminates duplicate values. (pi) symbol is used to choose attributes from a relation. This operator helps you to keep specific columns from a relation and discards the other columns.

Question 3

Rename

Answer 3

Rename is a unary operation used for renaming attributes of a relation.

ρ (a/b)R will rename the attribute ‘b’ of relation by ‘a’.

Question 4

Cartesian Product

Answer 4

An operation used to merge columns from two relations. Generally, a cartesian product is never a meaningful operation when it performs alone. However, it becomes meaningful when it is followed by other operations. It is also called Cross Product or Cross Join.

Question 5

NATURAL JOIN

Answer 5

Natural join can only be performed if there is a common attribute (column) between the relations. The name and type of the attribute must be same. (⋈)

Question 6

Relational Algebra

Answer 6

Procedural Query Language which takes instances of relations as input and yields instances of relations as output.

Question 7

Relational Calculus

Answer 7

In contrast to Relational Algebra, Relational Calculus is a non-procedural query language, that is, it tells what to do but never explains how to do it.