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| author | Tomas Vondra <tomas.vondra@postgresql.org> | 2021-03-18 17:45:38 +0100 |
|---|---|---|
| committer | Tomas Vondra <tomas.vondra@postgresql.org> | 2021-03-18 18:22:18 +0100 |
| commit | be45be9c33a85e72cdaeb9967e9f6d2d00199e09 (patch) | |
| tree | c728067c32404e7475ebf4c66561d7edf2dd35b3 /src/include/nodes/pg_list.h | |
| parent | cd91de0d17952b5763466cfa663e98318f26d357 (diff) | |
| download | postgresql-be45be9c33a85e72cdaeb9967e9f6d2d00199e09.tar.gz postgresql-be45be9c33a85e72cdaeb9967e9f6d2d00199e09.zip | |
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
Diffstat (limited to 'src/include/nodes/pg_list.h')
| -rw-r--r-- | src/include/nodes/pg_list.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/src/include/nodes/pg_list.h b/src/include/nodes/pg_list.h index 404e03f132d..30f98c4595f 100644 --- a/src/include/nodes/pg_list.h +++ b/src/include/nodes/pg_list.h @@ -604,6 +604,7 @@ extern pg_nodiscard List *list_copy_deep(const List *oldlist); typedef int (*list_sort_comparator) (const ListCell *a, const ListCell *b); extern void list_sort(List *list, list_sort_comparator cmp); +extern int list_int_cmp(const ListCell *p1, const ListCell *p2); extern int list_oid_cmp(const ListCell *p1, const ListCell *p2); #endif /* PG_LIST_H */ |