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Fix an oversight in checking whether a join with LATERAL refs is legal.

2015年7月31日 23:26:33 +0000 (19:26 -0400)

In many cases, we can implement a semijoin as a plain innerjoin by first
passing the righthand-side relation through a unique-ification step.
However, one of the cases where this does NOT work is where the RHS has
a LATERAL reference to the LHS; that makes the RHS dependent on the LHS
so that unique-ification is meaningless. joinpath.c understood this,
and so would not generate any join paths of this kind ... but join_is_legal
neglected to check for the case, so it would think that we could do it.
The upshot would be a "could not devise a query plan for the given query"
failure once we had failed to generate any join paths at all for the bogus
join pair.

Back-patch to 9.3 where LATERAL was added.

src/backend/optimizer/path/joinrels.c patch | blob | blame | history

src/test/regress/expected/join.out patch | blob | blame | history

src/test/regress/sql/join.sql patch | blob | blame | history

diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c

index fe9fd57317429c08d99c9c98f4c92af2728dff45..b6c9494fed67f7877507a5dd4763fbb70194ec21 100644 (file)

--- a/src/backend/optimizer/path/joinrels.c

+++ b/src/backend/optimizer/path/joinrels.c

@@ -536,7 +536,9 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,

if (!bms_is_subset(ljinfo->lateral_lhs, rel1->relids))

return false; /* rel1 can't compute the required parameter */

if (match_sjinfo &&

- (reversed || match_sjinfo->jointype == JOIN_FULL))

+ (reversed ||

+ unique_ified ||

+ match_sjinfo->jointype == JOIN_FULL))

return false; /* not implementable as nestloop */

}

if (bms_is_subset(ljinfo->lateral_rhs, rel1->relids) &&

@@ -549,7 +551,9 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,

if (!bms_is_subset(ljinfo->lateral_lhs, rel2->relids))

return false; /* rel2 can't compute the required parameter */

if (match_sjinfo &&

- (!reversed || match_sjinfo->jointype == JOIN_FULL))

+ (!reversed ||

+ unique_ified ||

+ match_sjinfo->jointype == JOIN_FULL))

return false; /* not implementable as nestloop */

}

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out

index 1afd0c328b5b8c5c56861bb7e28216d6695ee1c7..10336d48a3adb89d3322bc49ec71857a2537bae9 100644 (file)

--- a/src/test/regress/expected/join.out

+++ b/src/test/regress/expected/join.out

@@ -4527,6 +4527,41 @@ select * from

Output: 3

(11 rows)

+-- check we don't try to do a unique-ified semijoin with LATERAL

+explain (verbose, costs off)

+select * from

+ (values (0,9998), (1,1000)) v(id,x),

+ lateral (select f1 from int4_tbl

+ where f1 = any (select unique1 from tenk1

+ where unique2 = v.x offset 0)) ss;

+ QUERY PLAN

+----------------------------------------------------------------------

+ Nested Loop

+ Output: "*VALUES*".column1, "*VALUES*".column2, int4_tbl.f1

+ -> Values Scan on "*VALUES*"

+ Output: "*VALUES*".column1, "*VALUES*".column2

+ -> Nested Loop Semi Join

+ Output: int4_tbl.f1

+ Join Filter: (int4_tbl.f1 = tenk1.unique1)

+ -> Seq Scan on public.int4_tbl

+ Output: int4_tbl.f1

+ -> Materialize

+ Output: tenk1.unique1

+ -> Index Scan using tenk1_unique2 on public.tenk1

+ Output: tenk1.unique1

+ Index Cond: (tenk1.unique2 = "*VALUES*".column2)

+(14 rows)

+select * from

+ (values (0,9998), (1,1000)) v(id,x),

+ lateral (select f1 from int4_tbl

+ where f1 = any (select unique1 from tenk1

+ where unique2 = v.x offset 0)) ss;

+ id | x | f1

+----+------+----

+ 0 | 9998 | 0

+(1 row)

-- test some error cases where LATERAL should have been used but wasn't

select f1,g from int4_tbl a, (select f1 as g) ss;

ERROR: column "f1" does not exist

diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql

index d34cefac5a18fb0e63562ea137abee70fc43d3be..7553aefc6bd72caa1033f846e8068963fa3465c2 100644 (file)

--- a/src/test/regress/sql/join.sql

+++ b/src/test/regress/sql/join.sql

@@ -1365,6 +1365,19 @@ select * from

select * from (select 3 as z offset 0) z where z.z = x.x

) zz on zz.z = y.y;

+-- check we don't try to do a unique-ified semijoin with LATERAL

+explain (verbose, costs off)

+select * from

+ (values (0,9998), (1,1000)) v(id,x),

+ lateral (select f1 from int4_tbl

+ where f1 = any (select unique1 from tenk1

+ where unique2 = v.x offset 0)) ss;

+select * from

+ (values (0,9998), (1,1000)) v(id,x),

+ lateral (select f1 from int4_tbl

+ where f1 = any (select unique1 from tenk1

+ where unique2 = v.x offset 0)) ss;

-- test some error cases where LATERAL should have been used but wasn't

select f1,g from int4_tbl a, (select f1 as g) ss;

select f1,g from int4_tbl a, (select a.f1 as g) ss;

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