subquery

MySQL Subquery

Summary: in this tutorial, we will show you how to use the MySQL subquery to write complex queries and explain the correlated subquery concept.

A MySQL subquery is a query nested within another query such as SELECT, INSERT, UPDATE or DELETE. In addition, a MySQL subquery can be nested inside another subquery.

A MySQL subquery is called an inner query while the query that contains the subquery is called an outer query. A subquery can be used anywhere that expression is used and must be closed in parentheses.

The following query returns employees who work in the offices located in the USA.

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SELECT     lastName, firstName FROM     employees WHERE     officeCode IN (SELECT             officeCode         FROM             offices         WHERE             country = 'USA');

Resource: http://www.mysqltutorial.org/mysql-subquery/