diff options
| -rw-r--r-- | src/backend/optimizer/prep/prepunion.c | 23 |
1 files changed, 11 insertions, 12 deletions
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c index e04ddf86cd5..3616ef1d65a 100644 --- a/src/backend/optimizer/prep/prepunion.c +++ b/src/backend/optimizer/prep/prepunion.c @@ -569,9 +569,9 @@ generate_union_paths(SetOperationStmt *op, PlannerInfo *root, /* * If any of my children are identical UNION nodes (same op, all-flag, and - * colTypes) then they can be merged into this node so that we generate - * only one Append and unique-ification for the lot. Recurse to find such - * nodes and compute their children's paths. + * colTypes/colCollations) then they can be merged into this node so that + * we generate only one Append and unique-ification for the lot. Recurse + * to find such nodes and compute their children's paths. */ rellist = plan_union_children(root, op, refnames_tlist, &tlist_list); @@ -860,17 +860,15 @@ generate_nonunion_paths(SetOperationStmt *op, PlannerInfo *root, } /* - * Pull up children of a UNION node that are identically-propertied UNIONs. + * Pull up children of a UNION node that are identically-propertied UNIONs, + * and perform planning of the queries underneath the N-way UNION. + * + * The result is a list of RelOptInfos containing Paths for sub-nodes, with + * one entry for each descendant that is a leaf query or non-identical setop. + * We also return a parallel list of the childrens' targetlists. * * NOTE: we can also pull a UNION ALL up into a UNION, since the distinct * output rows will be lost anyway. - * - * NOTE: currently, we ignore collations while determining if a child has - * the same properties. This is semantically sound only so long as all - * collations have the same notion of equality. It is valid from an - * implementation standpoint because we don't care about the ordering of - * a UNION child's result: UNION ALL results are always unordered, and - * generate_union_paths will force a fresh sort if the top level is a UNION. */ static List * plan_union_children(PlannerInfo *root, @@ -896,7 +894,8 @@ plan_union_children(PlannerInfo *root, if (op->op == top_union->op && (op->all == top_union->all || op->all) && - equal(op->colTypes, top_union->colTypes)) + equal(op->colTypes, top_union->colTypes) && + equal(op->colCollations, top_union->colCollations)) { /* Same UNION, so fold children into parent */ pending_rels = lcons(op->rarg, pending_rels); |