MySQL Sub Query with Exists and Not Exists Important Concept

Table of Contents

MySQL Sub Query:

MySQL Sub Query is a query nested within another query such as SELECT, INSERT, UPDATE or DELETE.

When a subquery is used with the EXISTS or NOT EXISTS operator, a subquery returns a Boolean value of TRUE or FALSE.

SELECT column_name (s)
FROM table1
WHERE
(SELECT column_name FROM table2)

SELECT column_name (s)
FROM table1
WHERE EXISTS
(SELECT column_name FROM table2)

SELECT column_name (s)
FROM table1
WHERE NOT EXISTS
(SELECT column_name FROM table2)

If cn_name (London) exists in the city table, then it will fetch all data of the field (name) contained in the student table.

If cn_name (England) not exists in the city table, then it will fetch all data of the field (name) contained in the student table.