The following subquery restrictions have been removed:
You can use distinct with group by in a subquery.
The distinct keyword suppressed duplicate rows in the output of pre-release 10.0 subqueries. This keyword is no longer necessary, and is ignored, in subqueries.
You can reference a correlated variable in the select list of a subquery. For example, the following expression subquery is now supported:
select t1.c1 from t1
where t1.c2 = (select t2.c2 + t1.c3 from t2)
The following subquery restriction has been added:
There is a maximum of 16 subqueries within a single side of a union.
