Tom> As a stopgap measure, I think what we have to do is teach Tom> check_output_expressions that subquery output columns are unsafe Tom> to reference if they are not listed in all grouping sets (do I Tom> have that condition right?).
Unless I'm missing something, it should be safe to reference output columns that are not mentioned in any grouping set,
I think such columns usually are aggregation expr, If we want to push down
a qual which reference to an aggregation expr, we have to push down
to having cause, However I am not sure such pushing down really helps.
or which are mentioned in all grouping sets (after all expansions);
