Finish incomplete revert of ec63622c0.

The code change this made might well be fine to keep, but the
comment justifying it by reference to self-join removal isn't.
Let's just go back to the status quo ante, pending a more thorough
review/redesign of SJE.

(I found this by grepping to see if any references to self-join
removal remained in the tree.)
This commit is contained in:
Tom Lane 2024-05-06 14:22:45 -04:00
parent 521a7156ab
commit 07746a8ef2
1 changed files with 3 additions and 6 deletions

View File

@ -662,17 +662,14 @@ build_setop_child_paths(PlannerInfo *root, RelOptInfo *rel,
* otherwise do statistical estimation.
*
* XXX you don't really want to know about this: we do the estimation
* using the subroot->parse's original targetlist expressions, not the
* using the subquery's original targetlist expressions, not the
* subroot->processed_tlist which might seem more appropriate. The reason
* is that if the subquery is itself a setop, it may return a
* processed_tlist containing "varno 0" Vars generated by
* generate_append_tlist, and those would confuse estimate_num_groups
* mightily. We ought to get rid of the "varno 0" hack, but that requires
* a redesign of the parsetree representation of setops, so that there can
* be an RTE corresponding to each setop's output. Note, we use this not
* subquery's targetlist but subroot->parse's targetlist, because it was
* revised by self-join removal. subquery's targetlist might contain the
* references to the removed relids.
* be an RTE corresponding to each setop's output.
*/
if (pNumGroups)
{
@ -685,7 +682,7 @@ build_setop_child_paths(PlannerInfo *root, RelOptInfo *rel,
*pNumGroups = rel->cheapest_total_path->rows;
else
*pNumGroups = estimate_num_groups(subroot,
get_tlist_exprs(subroot->parse->targetList, false),
get_tlist_exprs(subquery->targetList, false),
rel->cheapest_total_path->rows,
NULL,
NULL);