pgsql: Determine grouping strategies in create_grouping_paths.

Determine grouping strategies in create_grouping_paths.

Partition-wise aggregate will call create_ordinary_grouping_paths
multiple times and we don't want to redo this work every time; have
the caller do it instead and pass the details down.

Patch by me, reviewed by Ashutosh Bapat.

Discussion: http://postgr.es/m/CA+TgmoY7VYYn9a7YHj1nJL6zj6BkHmt4K-un9LRmXkyqRZyynA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b5996c2791f36a79332e3cb7130e9125a0372730

Modified Files
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src/backend/optimizer/plan/planner.c | 142 ++++++++++++++++++++---------------
1 file changed, 82 insertions(+), 60 deletions(-)