From be45be9c33a85e72cdaeb9967e9f6d2d00199e09 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Thu, 18 Mar 2021 17:45:38 +0100 Subject: Implement GROUP BY DISTINCT With grouping sets, it's possible that some of the grouping sets are duplicate. This is especially common with CUBE and ROLLUP clauses. For example GROUP BY CUBE (a,b), CUBE (b,c) is equivalent to GROUP BY GROUPING SETS ( (a, b, c), (a, b, c), (a, b, c), (a, b), (a, b), (a, b), (a), (a), (a), (c, a), (c, a), (c, a), (c), (b, c), (b), () ) Some of the grouping sets are calculated multiple times, which is mostly unnecessary. This commit implements a new GROUP BY DISTINCT feature, as defined in the SQL standard, which eliminates the duplicate sets. Author: Vik Fearing Reviewed-by: Erik Rijkers, Georgios Kokolatos, Tomas Vondra Discussion: https://postgr.es/m/bf3805a8-d7d1-ae61-fece-761b7ff41ecc@postgresfriends.org --- src/backend/utils/adt/ruleutils.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'src/backend/utils/adt/ruleutils.c') diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c index 879288c1394..f0de2a25c96 100644 --- a/src/backend/utils/adt/ruleutils.c +++ b/src/backend/utils/adt/ruleutils.c @@ -5517,6 +5517,8 @@ get_basic_select_query(Query *query, deparse_context *context, appendContextKeyword(context, " GROUP BY ", -PRETTYINDENT_STD, PRETTYINDENT_STD, 1); + if (query->groupDistinct) + appendStringInfoString(buf, "DISTINCT "); save_exprkind = context->special_exprkind; context->special_exprkind = EXPR_KIND_GROUP_BY; -- cgit v1.2.3