Fix thinko in join removal.

In commit 9df8f903e I (tgl) switched join_is_removable() from
using the min relid sets of the join under consideration to
using its full syntactic relid sets.  This was a mistake,
as it allowed join removal in cases where a reference to the
join output would survive in some syntactically-lower join
condition.  Revert to the former coding.

Richard Guo

Discussion: https://postgr.es/m/CAMbWs4-EU9uBGSP7G-iTwLBhRQ=rnZKvFDhD+n+xhajokyPCKg@mail.gmail.com

diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 7463b3696ac926f136cdc8f73e5b383199d873c8..a61e35f92d068582cfa146aabbe12968553ab2ae 100644 (file)
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -88,11 +88,8 @@ restart:
                 */
                innerrelid = bms_singleton_member(sjinfo->min_righthand);
 
-               /*
-                * Compute the relid set for the join we are considering.  We can
-                * assume things are done in syntactic order.
-                */
-               joinrelids = bms_union(sjinfo->syn_lefthand, sjinfo->syn_righthand);
+               /* Compute the relid set for the join we are considering */
+               joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
                if (sjinfo->ojrelid != 0)
                        joinrelids = bms_add_member(joinrelids, sjinfo->ojrelid);
 
@@ -204,8 +201,8 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
        if (!rel_supports_distinctness(root, innerrel))
                return false;
 
-       /* Compute the syntactic relid set for the join we are considering */
-       inputrelids = bms_union(sjinfo->syn_lefthand, sjinfo->syn_righthand);
+       /* Compute the relid set for the join we are considering */
+       inputrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
        Assert(sjinfo->ojrelid != 0);
        joinrelids = bms_copy(inputrelids);
        joinrelids = bms_add_member(joinrelids, sjinfo->ojrelid);

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 9bafadde66fcfe3a2ae32fc634e531bb7b42d5f2..8fa2b376f3aaca4792bc57c82ce56ac411190a0a 100644 (file)
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -5432,6 +5432,22 @@ select d.* from d left join (select distinct * from b) s
          ->  Seq Scan on d
 (9 rows)
 
+-- join removal is not possible here
+explain (costs off)
+select 1 from a t1
+  left join (a t2 left join a t3 on t2.id = 1) on t2.id = 1;
+                       QUERY PLAN                       
+--------------------------------------------------------
+ Nested Loop Left Join
+   ->  Seq Scan on a t1
+   ->  Materialize
+         ->  Nested Loop Left Join
+               Join Filter: (t2.id = 1)
+               ->  Index Only Scan using a_pkey on a t2
+                     Index Cond: (id = 1)
+               ->  Seq Scan on a t3
+(8 rows)
+
 -- check join removal works when uniqueness of the join condition is enforced
 -- by a UNION
 explain (costs off)

diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index a44234b0af7449d45f8994ed09769f4aace9425b..641fd1a21b9f78cf9772f9569ff7b21d946e0eea 100644 (file)
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -1958,6 +1958,11 @@ explain (costs off)
 select d.* from d left join (select distinct * from b) s
   on d.a = s.id;
 
+-- join removal is not possible here
+explain (costs off)
+select 1 from a t1
+  left join (a t2 left join a t3 on t2.id = 1) on t2.id = 1;
+
 -- check join removal works when uniqueness of the join condition is enforced
 -- by a UNION
 explain (costs off)