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Commit232019b

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Don't remove surplus columns from GROUP BY for inheritance parents
d4c3a15 added code to remove columns that were not part of a table'sPRIMARY KEY constraint from the GROUP BY clause when all the primary keycolumns were present in the group by. This is fine to do since we knowthat there will only be one row per group coming from this relation.However, the logic failed to consider inheritance parent relations. Thesecan have child relations without a primary key, but even if they did, theycould duplicate one of the parent's rows or one from another childrelation. In this case, those additional GROUP BY columns are required.Fix this by disabling the optimization for inheritance parent tables.In v11 and beyond, partitioned tables are fine since partitions cannotoverlap and before v11 partitioned tables could not have a primary key.Reported-by: Manuel RiggerDiscussion:http://postgr.es/m/CA+u7OA7VLKf_vEr6kLF3MnWSA9LToJYncgpNX2tQ-oWzYCBQAw@mail.gmail.comBackpatch-through: 9.6
1 parent0ce8e49 commit232019b

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3 files changed

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-2
lines changed

3 files changed

+40
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lines changed

‎src/backend/optimizer/plan/planner.c

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2849,6 +2849,14 @@ remove_useless_groupby_columns(PlannerInfo *root)
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if (rte->rtekind!=RTE_RELATION)
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continue;
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/*
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* We must skip inheritance parent tables as some of the child rels
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* may cause duplicate rows. We can skip partitioned tables too since
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* these cannot have a primary key.
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*/
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if (rte->inh)
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continue;
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/* Nothing to do unless this rel has multiple Vars in GROUP BY */
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relattnos=groupbyattnos[relid];
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if (bms_membership(relattnos)!=BMS_MULTIPLE)

‎src/test/regress/expected/aggregates.out

Lines changed: 23 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1017,7 +1017,29 @@ explain (costs off) select * from t3 group by a,b,c;
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-> Seq Scan on t3
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(3 rows)
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drop table t1;
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create temp table t1c () inherits (t1);
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-- Ensure we don't remove any columns when t1 has a child table
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explain (costs off) select * from t1 group by a,b,c,d;
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QUERY PLAN
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-------------------------------------
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HashAggregate
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Group Key: t1.a, t1.b, t1.c, t1.d
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-> Append
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-> Seq Scan on t1
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-> Seq Scan on t1c
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(5 rows)
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-- Okay to remove columns if we're only querying the parent.
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explain (costs off) select * from only t1 group by a,b,c,d;
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QUERY PLAN
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----------------------
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HashAggregate
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Group Key: a, b
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-> Seq Scan on t1
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(3 rows)
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drop table t1 cascade;
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NOTICE: drop cascades to table t1c
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drop table t2;
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drop table t3;
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--

‎src/test/regress/sql/aggregates.sql

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -362,7 +362,15 @@ group by t1.a,t1.b,t1.c,t1.d,t2.x,t2.z;
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-- Cannot optimize when PK is deferrable
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explain (costs off)select*from t3group by a,b,c;
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droptable t1;
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create temp table t1c () inherits (t1);
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-- Ensure we don't remove any columns when t1 has a child table
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explain (costs off)select*from t1group by a,b,c,d;
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-- Okay to remove columns if we're only querying the parent.
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explain (costs off)select*from only t1group by a,b,c,d;
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droptable t1 cascade;
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droptable t2;
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droptable t3;
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