pgsql: Simplify PathKey checking code

Simplify PathKey checking code

pathkeys_useful_for_ordering() contained some needless checks to return
0 when either root->query_pathkeys or pathkeys lists were empty. This is
already handled by pathkeys_count_contained_in(), so let's have it do the
work instead of having redundant checks.

Similarly, in pathkeys_useful_for_grouping(), checking pathkeys is an
empty list just before looping over it isn't required. Technically,
neither is the list empty check for group_pathkeys, but I felt a bit
more work would have to be done to get the equivalent behavior if we'd
left it up to the foreach loop to call list_member_ptr().

This was noticed by Andy while he was reviewing a patch to improve the
UNION planner. Since that patch adds another function similar to
pathkeys_useful_for_ordering() and since I wasn't planning to copy these
redundant checks over to the new function, let's adjust the existing
code so that both functions will be consistent.

Author: Andy Fan
Discussion: https://postgr.es/m/87o7cti48f.fsf@163.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0c444a70f2a79d4d7ef6f1af057909839e5b2097

Modified Files
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src/backend/optimizer/path/pathkeys.c | 10 ----------
1 file changed, 10 deletions(-)