From 8d3c4aa614e20375daeff0bb1b9f640b115f363e Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 22 Mar 2010 13:57:16 +0000
Subject: [PATCH] Fix an oversight in join-removal optimization: we have to
check not only for plain Vars that are generated in the inner rel and used
above the join, but also for PlaceHolderVars. Per report from Oleg K.
---
src/backend/optimizer/path/joinpath.c | 19 +++++++++--
src/test/regress/expected/join.out | 49 +++++++++++++++++++++++++++
src/test/regress/sql/join.sql | 23 +++++++++++++
3 files changed, 89 insertions(+), 2 deletions(-)
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index 35c9353d2e2..f069f13fefb 100644
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.130 2010/02/26 02:00:44 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.131 2010/03/22 13:57:15 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -192,7 +192,9 @@ clause_sides_match_join(RestrictInfo *rinfo, RelOptInfo *outerrel,
*
* This is true for a left join for which the join condition cannot match
* more than one inner-side row. (There are other possibly interesting
- * cases, but we don't have the infrastructure to prove them.)
+ * cases, but we don't have the infrastructure to prove them.) We also
+ * have to check that the inner side doesn't generate any variables needed
+ * above the join.
*
* Note: there is no need to consider the symmetrical case of duplicating the
* right input, because add_paths_to_joinrel() will be called with each rel
@@ -245,6 +247,19 @@ join_is_removable(PlannerInfo *root,
return false;
}
+ /*
+ * Similarly check that the inner rel doesn't produce any PlaceHolderVars
+ * that will be used above the join.
+ */
+ foreach(l, root->placeholder_list)
+ {
+ PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
+
+ if (bms_is_subset(phinfo->ph_eval_at, innerrel->relids) &&
+ !bms_is_subset(phinfo->ph_needed, joinrel->relids))
+ return false;
+ }
+
/*
* Search for mergejoinable clauses that constrain the inner rel against
* either the outer rel or a pseudoconstant. If an operator is
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index f2b346e5084..ad164e1c02b 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -2491,3 +2491,52 @@ select * from int4_tbl a full join int4_tbl b on false;
-2147483647 |
(10 rows)
+--
+-- test join removal
+--
+create temp table parent (k int primary key, pd int);
+NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "parent_pkey" for table "parent"
+create temp table child (k int unique, cd int);
+NOTICE: CREATE TABLE / UNIQUE will create implicit index "child_k_key" for table "child"
+insert into parent values (1, 10), (2, 20), (3, 30);
+insert into child values (1, 100), (4, 400);
+-- this case is optimizable
+select p.* from parent p left join child c on (p.k = c.k);
+ k | pd
+---+----
+ 1 | 10
+ 2 | 20
+ 3 | 30
+(3 rows)
+
+explain (costs off)
+ select p.* from parent p left join child c on (p.k = c.k);
+ QUERY PLAN
+----------------------
+ Seq Scan on parent p
+(1 row)
+
+-- this case is not
+select p.*, linked from parent p
+ left join (select c.*, true as linked from child c) as ss
+ on (p.k = ss.k);
+ k | pd | linked
+---+----+--------
+ 1 | 10 | t
+ 2 | 20 |
+ 3 | 30 |
+(3 rows)
+
+explain (costs off)
+ select p.*, linked from parent p
+ left join (select c.*, true as linked from child c) as ss
+ on (p.k = ss.k);
+ QUERY PLAN
+---------------------------------
+ Hash Left Join
+ Hash Cond: (p.k = c.k)
+ -> Seq Scan on parent p
+ -> Hash
+ -> Seq Scan on child c
+(5 rows)
+
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 977765551d5..b0a4ceccf0b 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -567,3 +567,26 @@ group by t1.q2 order by 1;
--
select * from int4_tbl a full join int4_tbl b on true;
select * from int4_tbl a full join int4_tbl b on false;
+
+--
+-- test join removal
+--
+
+create temp table parent (k int primary key, pd int);
+create temp table child (k int unique, cd int);
+insert into parent values (1, 10), (2, 20), (3, 30);
+insert into child values (1, 100), (4, 400);
+
+-- this case is optimizable
+select p.* from parent p left join child c on (p.k = c.k);
+explain (costs off)
+ select p.* from parent p left join child c on (p.k = c.k);
+
+-- this case is not
+select p.*, linked from parent p
+ left join (select c.*, true as linked from child c) as ss
+ on (p.k = ss.k);
+explain (costs off)
+ select p.*, linked from parent p
+ left join (select c.*, true as linked from child c) as ss
+ on (p.k = ss.k);
--
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