diff options
Diffstat (limited to 'src/backend')
| -rw-r--r-- | src/backend/optimizer/prep/prepunion.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c index b5cb4de6a26..881d85e26cc 100644 --- a/src/backend/optimizer/prep/prepunion.c +++ b/src/backend/optimizer/prep/prepunion.c @@ -337,6 +337,16 @@ recurse_set_operations(Node *setOp, PlannerInfo *root, * Estimate number of groups if caller wants it. If the subquery used * grouping or aggregation, its output is probably mostly unique * anyway; otherwise do statistical estimation. + * + * XXX you don't really want to know about this: we do the estimation + * 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. */ if (pNumGroups) { @@ -346,7 +356,7 @@ recurse_set_operations(Node *setOp, PlannerInfo *root, *pNumGroups = subpath->rows; else *pNumGroups = estimate_num_groups(subroot, - get_tlist_exprs(subroot->processed_tlist, false), + get_tlist_exprs(subquery->targetList, false), subpath->rows, NULL); } |