Subqueries are generally used to return a single row as an atomic value although they may be used to compare values against multiple rows with the IN keyword.

子查询一般用来返回一个单独的行作为原子值，然而还可以用来比较多行的值，利用IN关键字。

youdao

Subqueries are generally used to return a single row as an atomic value although they may be used to compare values against multiple rows with the IN keyword.

子查询一般用来返回一个单独的行作为原子值，然而还可以用来比较多行的值，利用IN关键字。

youdao