Major Description
Currently CollapseProject combines Project with Aggregate when the shared attributes are deterministic. But if there are correlated scalar subqueries in the project list that uses the output of the aggregate, they cannot be combined. Otherwise, the plan after rewrite will not be valid:
select (select sum(c2) from t where c1 = cast(s as int)) from (select sum(c2) s from t) == Optimized Logical Plan == Aggregate [sum(c2)#10L AS scalarsubquery(s)#11L] +- Project [sum(c2)#10L] +- Join LeftOuter, (c1#2 = cast(sum(c2#3) as int)) :- LocalRelation [c2#3] +- Aggregate [c1#2], [sum(c2#3) AS sum(c2)#10L, c1#2] +- LocalRelation [c1#2, c2#3] java.lang.UnsupportedOperationException: Cannot generate code for expression: sum(input[0, int, false])
