pgsql: Fix usage of aggregate pathkeys in group_keys_reorder_by_pathkey

Fix usage of aggregate pathkeys in group_keys_reorder_by_pathkeys()

group_keys_reorder_by_pathkeys() function searched for matching pathkeys
within root->group_pathkeys.  That could lead to picking an aggregate pathkey
and using its pathkey->pk_eclass->ec_sortref as an argument of
get_sortgroupref_clause_noerr().  Given that ec_sortref of an aggregate pathkey
references aggregate targetlist not query targetlist, this leads to incorrect
query optimization.

Fix this by looking for matching pathkeys only within the first
num_groupby_pathkeys pathkeys.

Reported-by: David G. Johnston
Discussion: https://postgr.es/m/CAKFQuwY3Ek%3DcLThgd8FdaSc5JRDVt0FaV00gMcWra%2BTAR4gGUw%40mail.gmail.com
Author: Andrei Lepikhov, Alexander Korotkov

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c01f6ef46c8f0ab3faa54e8f040da6e9ddc7fe5b

Modified Files
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src/backend/optimizer/path/pathkeys.c    | 25 +++++++++++++++++++++----
src/test/regress/expected/aggregates.out | 24 ++++++++++++++++++++++++
src/test/regress/sql/aggregates.sql      | 19 +++++++++++++++++++
3 files changed, 64 insertions(+), 4 deletions(-)