On 9/1/22 17:24, Richard Guo wrote:
On Wed, Aug 31, 2022 at 2:35 PM Andrey Lepikhov
<a.lepik...@postgrespro.ru <mailto:a.lepik...@postgrespro.ru>> wrote:
Before flattening procedure we just look through the quals of subquery,
pull to the upper level OpExpr's containing variables from the upper
relation and replace their positions in the quals with true expression.
Further, the flattening machinery works as usual.
Hmm, I'm not sure this patch works correctly in all cases. It seems to
me this patch pulls up the subquery without checking the constraints
imposed by lateral references. If its quals contain any lateral
references to rels outside a higher outer join, we would need to
postpone quals from below an outer join to above it, which is probably
incorrect.Yeah, it's not easy-to-solve problem. If I correctly understand the
code, to fix this problem we must implement the same logic, as
pull_up_subqueries (lowest_outer_join/safe_upper_varnos). It looks ugly.
But, more important, does this feature deserve such efforts/changes?
--
Regards
Andrey Lepikhov
Postgres Professional
