Subquery

A Select statement under the select statement is called a subquery. This sub statement can be used to select the column or in conditional cases. A subquery can also be nested within another query statement like INSERT, UPDATE, or DELETE.

The following query returns a set of users who are located in Ahmedabad using a subquery:

SELECT firstName, lastName FROM users 
WHERE city IN 
(SELECT city FROM cities WHERE city = 'Ahmedabad');