expression comparison_operator [ANY | ALL | SOME] (subquery)expression [NOT] IN (subquery)[NOT] EXISTS (subquery)
(SELECT [ALL | DISTINCT] subquery_select_list
[FROM {table_name | view_name}[optimizer_hints]
[[, {table_name2 | view_name2}[optimizer_hints]
[..., {table_name16 | view_name16}[optimizer_hints]]]
[WHERE clause]
[GROUP BY clause]
[HAVING clause])
Позапросы могут быть использованы помимо всего прочего и как выражения. Пример
declare @a varchar(80)
select @a=(select first_name from employee ...)+
получает +
(select convert(sum(pay)) from pays...)