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Fix out-dated comment in preprocess_groupclause()

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The comment claimed we don't consider other orders of the GROUP BY clause,
but this is no longer true as of db0d67db2.

Discussion: https://postgr.es/m/CAApHDvq65=9Ro+hLX1i9ugWEiNDvHrBibAO7ARcTnf38_JE+UQ@mail.gmail.com
Backpatch-through: 15, where db0d67db2 was introduced.
This commit is contained in:
David Rowley 2022-09-20 09:13:49 +12:00
parent 66fa8ff637
commit 78a9af1a27
1 changed files with 3 additions and 2 deletions
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5
src/backend/optimizer/plan/planner.c
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@ -2758,8 +2758,9 @@ remove_useless_groupby_columns(PlannerInfo *root)
*
* In principle it might be interesting to consider other orderings of the
* GROUP BY elements, which could match the sort ordering of other
* possible plans (eg an indexscan) and thereby reduce cost. We don't
* bother with that, though. Hashed grouping will frequently win anyway.
* possible plans (eg an indexscan) and thereby reduce cost. However, we
* don't yet have sufficient information to do that here, so that's left until
* later in planning. See get_useful_group_keys_orderings().
*
* Note: we need no comparable processing of the distinctClause because
* the parser already enforced that that matches ORDER BY.