A TableSubquery is a subquery that returns
multiple rows.
Unlike a ScalarSubquery, a TableSubquery is allowed only:
- as a TableExpression in
a FROM clause
- with EXISTS, IN, or quantified comparisons.
When used as a TableExpression in a FROM clause, it can return
multiple columns. When used with EXISTS, it returns multiple columns only
if you use * to return the multiple columns.
When used with IN or quantified
comparisons, it must return a single column.