diff options
Diffstat (limited to 'src/backend/optimizer/prep/prepunion.c')
| -rw-r--r-- | src/backend/optimizer/prep/prepunion.c | 23 |
1 files changed, 13 insertions, 10 deletions
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c index 72539545656..f528f096a56 100644 --- a/src/backend/optimizer/prep/prepunion.c +++ b/src/backend/optimizer/prep/prepunion.c @@ -901,19 +901,22 @@ generate_union_paths(SetOperationStmt *op, PlannerInfo *root, double dNumGroups; bool can_sort = grouping_is_sortable(groupList); bool can_hash = grouping_is_hashable(groupList); + Path *first_path = linitial(cheapest_pathlist); - if (list_length(cheapest_pathlist) == 1) + /* + * Estimate the number of UNION output rows. In the case when only a + * single UNION child remains, we can use estimate_num_groups() on + * that child. We must be careful not to do this when that child is + * the result of some other set operation as the targetlist will + * contain Vars with varno==0, which estimate_num_groups() wouldn't + * like. + */ + if (list_length(cheapest_pathlist) == 1 && + first_path->parent->reloptkind != RELOPT_UPPER_REL) { - Path *path = linitial(cheapest_pathlist); - - /* - * In the case where only one union child remains due to the - * detection of one or more dummy union children, obtain an - * estimate on the surviving child directly. - */ dNumGroups = estimate_num_groups(root, - path->pathtarget->exprs, - path->rows, + first_path->pathtarget->exprs, + first_path->rows, NULL, NULL); } |