MySQL subquery subquery

A subquery (subquery) refers to a SELECT clause that appears within other SQL statements.

For example:

SELECT * from t1 where col1= (select col2 from T2);

where select * from T1, called Outer query/outer Statement (outer query)

Select col2 from T2, called subquery (subquery)

The subquery must be nested inside the query and must always appear inside the parentheses

A subquery can contain more than one keyword or condition,

such as the distinct group by order by limit function, etc.

The outer query of a subquery can be a SELECT Insert update set or do

Subquery return value

A subquery can return a scalar, a row, a column, or a subquery.

MySQL subquery subquery