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Commitd0f9526

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Fix thinko in join removal.
In commit9df8f90 I (tgl) switched join_is_removable() fromusing the min relid sets of the join under consideration tousing its full syntactic relid sets. This was a mistake,as it allowed join removal in cases where a reference to thejoin output would survive in some syntactically-lower joincondition. Revert to the former coding.Richard GuoDiscussion:https://postgr.es/m/CAMbWs4-EU9uBGSP7G-iTwLBhRQ=rnZKvFDhD+n+xhajokyPCKg@mail.gmail.com
1 parent70b42f2 commitd0f9526

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3 files changed

+25
-7
lines changed

3 files changed

+25
-7
lines changed

‎src/backend/optimizer/plan/analyzejoins.c

Lines changed: 4 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -88,11 +88,8 @@ remove_useless_joins(PlannerInfo *root, List *joinlist)
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*/
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innerrelid=bms_singleton_member(sjinfo->min_righthand);
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91-
/*
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* Compute the relid set for the join we are considering. We can
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* assume things are done in syntactic order.
94-
*/
95-
joinrelids=bms_union(sjinfo->syn_lefthand,sjinfo->syn_righthand);
91+
/* Compute the relid set for the join we are considering */
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joinrelids=bms_union(sjinfo->min_lefthand,sjinfo->min_righthand);
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if (sjinfo->ojrelid!=0)
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joinrelids=bms_add_member(joinrelids,sjinfo->ojrelid);
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@@ -204,8 +201,8 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
204201
if (!rel_supports_distinctness(root,innerrel))
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return false;
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207-
/* Compute thesyntacticrelid set for the join we are considering */
208-
inputrelids=bms_union(sjinfo->syn_lefthand,sjinfo->syn_righthand);
204+
/* Compute the relid set for the join we are considering */
205+
inputrelids=bms_union(sjinfo->min_lefthand,sjinfo->min_righthand);
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Assert(sjinfo->ojrelid!=0);
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joinrelids=bms_copy(inputrelids);
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joinrelids=bms_add_member(joinrelids,sjinfo->ojrelid);

‎src/test/regress/expected/join.out

Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5432,6 +5432,22 @@ select d.* from d left join (select distinct * from b) s
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-> Seq Scan on d
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(9 rows)
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5435+
-- join removal is not possible here
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explain (costs off)
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select 1 from a t1
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left join (a t2 left join a t3 on t2.id = 1) on t2.id = 1;
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QUERY PLAN
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--------------------------------------------------------
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Nested Loop Left Join
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-> Seq Scan on a t1
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-> Materialize
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-> Nested Loop Left Join
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Join Filter: (t2.id = 1)
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-> Index Only Scan using a_pkey on a t2
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Index Cond: (id = 1)
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-> Seq Scan on a t3
5449+
(8 rows)
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-- check join removal works when uniqueness of the join condition is enforced
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-- by a UNION
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explain (costs off)

‎src/test/regress/sql/join.sql

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1958,6 +1958,11 @@ explain (costs off)
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select d.*from dleft join (select distinct*from b) s
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ond.a=s.id;
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1961+
-- join removal is not possible here
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explain (costs off)
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select1from a t1
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left join (a t2left join a t3ont2.id=1)ont2.id=1;
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-- check join removal works when uniqueness of the join condition is enforced
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-- by a UNION
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explain (costs off)

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