Question

What is a subquery?

(a) A subquery is a select-from-where expression that is nested within another query

(b) A subquery is any query that is nested within another query

(c) A subquery is a relation that is externally specified which can be used to handle data in queries

(d) A subquery is a condition that excludes all the invalid tuples from the database

I got this question in an interview for job.

This intriguing question comes from Nested Subqueries in portion Introduction to Relational Model and Sql of RDBMS

Answer 1

Correct answer is (a) A subquery is a select-from-where expression that is nested within another query

Explanation: A subquery is a select-from-where expression that is nested within another query. Common uses for sub-queries are to perform tests for set membership, make set comparisons etc.