Restore preprocess_groupclause()

0452b461bc made optimizer explore alternative orderings of group-by pathkeys.
It eliminated preprocess_groupclause(), which was intended to match items
between GROUP BY and ORDER BY.  Instead, get_useful_group_keys_orderings()
function generates orderings of GROUP BY elements at the time of grouping
paths generation.  The get_useful_group_keys_orderings() function takes into
account 3 orderings of GROUP BY pathkeys and clauses: original order as written
in GROUP BY, matching ORDER BY clauses as much as possible, and matching the
input path as much as possible.  Given that even before 0452b461b,
preprocess_groupclause() could change the original order of GROUP BY clauses
we don't need to consider it apart from ordering matching ORDER BY clauses.

This commit restores preprocess_groupclause() to provide an ordering of
GROUP BY elements matching ORDER BY before generation of paths.  The new
version of preprocess_groupclause() takes into account an incremental sort.
The get_useful_group_keys_orderings() function now takes into 2 orderings of
GROUP BY elements: the order generated preprocess_groupclause() and the order
matching the input path as much as possible.

Discussion: https://postgr.es/m/CAPpHfdvyWLMGwvxaf%3D7KAp-z-4mxbSH8ti2f6mNOQv5metZFzg%40mail.gmail.com
Author: Alexander Korotkov
Reviewed-by: Andrei Lepikhov, Pavel Borisov

1 files changed, 3 insertions, 3 deletions

diff --git a/src/test/regress/expected/partition_aggregate.out b/src/test/regress/expected/partition_aggregate.out
index 1b900fddf8e..5f2c0cf5786 100644
--- a/src/test/regress/expected/partition_aggregate.out
+++ b/src/test/regress/expected/partition_aggregate.out
@@ -901,15 +901,15 @@ SELECT a, c, sum(b), avg(c), count(*) FROM pagg_tab_m GROUP BY (a+b)/2, 2, 1 HAV
    Sort Key: pagg_tab_m.a, pagg_tab_m.c, (sum(pagg_tab_m.b))
    ->  Append
          ->  HashAggregate
-               Group Key: ((pagg_tab_m.a + pagg_tab_m.b) / 2), pagg_tab_m.c, pagg_tab_m.a
+               Group Key: pagg_tab_m.a, pagg_tab_m.c, ((pagg_tab_m.a + pagg_tab_m.b) / 2)
                Filter: ((sum(pagg_tab_m.b) = 50) AND (avg(pagg_tab_m.c) > '25'::numeric))
                ->  Seq Scan on pagg_tab_m_p1 pagg_tab_m
          ->  HashAggregate
-               Group Key: ((pagg_tab_m_1.a + pagg_tab_m_1.b) / 2), pagg_tab_m_1.c, pagg_tab_m_1.a
+               Group Key: pagg_tab_m_1.a, pagg_tab_m_1.c, ((pagg_tab_m_1.a + pagg_tab_m_1.b) / 2)
                Filter: ((sum(pagg_tab_m_1.b) = 50) AND (avg(pagg_tab_m_1.c) > '25'::numeric))
                ->  Seq Scan on pagg_tab_m_p2 pagg_tab_m_1
          ->  HashAggregate
-               Group Key: ((pagg_tab_m_2.a + pagg_tab_m_2.b) / 2), pagg_tab_m_2.c, pagg_tab_m_2.a
+               Group Key: pagg_tab_m_2.a, pagg_tab_m_2.c, ((pagg_tab_m_2.a + pagg_tab_m_2.b) / 2)
                Filter: ((sum(pagg_tab_m_2.b) = 50) AND (avg(pagg_tab_m_2.c) > '25'::numeric))
                ->  Seq Scan on pagg_tab_m_p3 pagg_tab_m_2
 (15 rows)