MySQL from sub-query

Sub-query in FROM clause

The MySQL from subquery refers to the FROM clause as a subquery statement, and the main query then obtains the required data in the subquery results. The FROM subquery syntax is as follows:

SELECT ... From (subquery) as name ...

A subquery generates a temporary table, because each table in the FROM clause must have a name, so as name is required. The from subquery is also known as a derived data table subquery.

From child query instance

Table1:

S1	S2
1	5
2	12
3	20

The From subquery SQL is as follows:

Select S1,s2 from (select S1, s2*2 as S2 from table1) as temp WHERE S1 > 1

The results of the query return are as follows:

S1	S2
2	24
3	40

Tips

A subquery in the MySQL FROM clause can return a scalar, column, row, or table, but not a subquery that has an associated query.

MySQL from sub-query