What are Subqueries?
A subquery, commonly referred to as a nested or inner query, is a query within another SQL statement, such as SELECT, INSERT, UPDATE, and DELETE that sometimes references an outer query. Rather, a subquery’s outcome can be utilized in different parts of the main query including the WHERE clause, FROM clause, or another subquery.
Syntax:
SELECT column1 FROM table1 WHERE column2 = (SELECT column3 FROM table2 WHERE condition);
Explanation: In this syntax, the subquery (SELECT column3 FROM table2 WHERE condition) is enclosed within parentheses and returns a single value. This value is then compared to column2 in the outer query’s WHERE clause.
Subqueries and EXISTS in MariaDB
Subqueries and EXISTS are powerful tools in MariaDB that enable us to write complex and efficient queries. Subqueries allow us to nest one query inside another and provide a flexible way to retrieve data. The EXISTS operator, on the other hand, it checks for the existence of rows returned by a subquery. In this article, we will look at what subqueries are, how they work, and how the EXISTS operator can be used to extend their functionality in MariaDB.