Question

What does the “x” operator do in relational algebra?

(a) Output specified attributes from all rows of the input relation. Remove duplicate tuples from the output

(b) Output pairs of rows from the two input relations that have the same value on all attributes that have the same name

(c) Output all pairs of rows from the two input relations (regardless of whether or not they have the same values on common attributes)

(d) Returns the rows of the input relation that satisfy the predicate

This question was posed to me in an international level competition.

This key question is from Introduction to the Relational Model topic in chapter Introduction to Relational Model and Sql of RDBMS

Answer 1

Correct choice is (c) Output all pairs of rows from the two input relations (regardless of whether or not they have the same values on common attributes)

Easy explanation: The “x” operator outputs all pairs of rows from the two input relations (regardless of whether or not they have the same values on common attributes). This operation is called as the Cartesian product operation and is similar to the Cartesian product of sets.