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Commitaf7d270

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Fix hypothetical problem passing the wrong GROUP BY pathkeys
1349d27 changed things to make the planner request that thequery_pathkeys contain pathkeys for any ORDER BY / DISTINCT aggregates.Some code added prior to that commit indb0d67d made it so the orderthat the pathkeys appear in the group_pathkeys could be changed so thatthe GROUP BY could be executed in a more optimal order which minimizedsort comparisons.1349d27 had to make sure that the pathkeys for anyORDER BY / DISTINCT aggregates remained at the end of the groupby_pathkeysand wasn't reordered, so some code was added toadd_paths_to_grouping_rel() to first strip off any pathkeys belonging toORDER BY / DISTINCT aggregates before passing to the function to optimizethe order of the group_pathkeys.It seems I dropped the ball in1349d27 and mistakenly used the untouchedPlannerInfo.group_pathkeys to pass to get_useful_group_keys_orderings()instead of the version that had the aggregate pathkeys removed. It wasonly the code path that was handling creating paths forpartially_grouped_rel which made this mistake. In practice, we'll neverhave any extra pathkeys to strip off when processingpartially_grouped_rel as that's only used when considering partialpaths, which we never do when there are ORDER BY / DISTINCT aggregates.So this is just a hypothetical bug, not a live bug. We already have thecorrect pathkeys determined, so it's of no extra cost to pass thecorrect variable.Reported-by: Justin PryzbyDiscussion:https://postgr.es/m/20220817015755.GB26426@telsasoft.com
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‎src/backend/optimizer/plan/planner.c

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@@ -6637,10 +6637,7 @@ add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
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ListCell*lc2;
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Path*path= (Path*)lfirst(lc);
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Path*path_original=path;
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List*pathkey_orderings=NIL;
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List*group_pathkeys=root->group_pathkeys;
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List*group_clauses=parse->groupClause;
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/* generate alternative group orderings that might be useful */

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