Relational Operators

Question 1

What is a relational operator?

Answer 1

A query language that allows tuples to be retrieved and updated in one statement without looping.

Question 2

What are the five fundamental operations?

Answer 2

Selection, projection, cartesian product, union and set difference.

Question 3

What are the Unary Operations?

Answer 3

Selection - works on a single relation R and defines a relation that contains only those tuples of R that satisfy the specified condition.

Projection - extracts the values of specified attributes and eliminating duplicates.

Question 4

What are the set operations?

Answer 4

Union, Set difference, cartesian product, intersection and join.

Question 5

What does a union operation do?

Answer 5

These contains all the tuples of R and S with duplicates eliminated. It is only possible if the two schemas have the same number of attributes.

Question 6

What does a set difference operation do?

Answer 6

This defines a relation consisting of the tuples that are in R but not in S.

Question 7

What does a intersection operation do?

Answer 7

This consists of the set of all tuples that are in both R and S.

Question 8

What does a cartesian product operation do?

Answer 8

This multiplies two relations to define another relation consisting of all possible pairs of tuples from the two relations.

Question 9

What are the six types of join operations?

Answer 9

Theta, equijoin, natural, outer, semi and division.