From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 1 Mar 2019 22:57:20 +0000 (-0500)
Subject: Check we don't misoptimize a NOT IN where the subquery returns no rows.
X-Git-Tag: REL_12_BETA1~636
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=3396138a6de329fa7b5e0dda79219b4ae82622dc;p=postgresql

Check we don't misoptimize a NOT IN where the subquery returns no rows.

Future-proofing against a common mistake in attempts to optimize NOT IN.
We don't have such an optimization right now, but attempts to do so
are in the works, and some of 'em are buggy.  Add a regression test case
covering the point.

David Rowley

Discussion: https://postgr.es/m/CAKJS1f90E9agVZryVyUpbHQbjTt5ExqS2Fsodmt5_A7E_cEyVA@mail.gmail.com
---

diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index cc3f5f3737..fe5fc64480 100644
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -830,6 +830,19 @@ explain (verbose, costs off)
                  One-Time Filter: ("*VALUES*".column1 = "*VALUES*".column1)
 (8 rows)
 
+--
+-- Check we don't misoptimize a NOT IN where the subquery returns no rows.
+--
+create temp table notinouter (a int);
+create temp table notininner (b int not null);
+insert into notinouter values (null), (1);
+select * from notinouter where a not in (select b from notininner);
+ a 
+---
+  
+ 1
+(2 rows)
+
 --
 -- Check we behave sanely in corner case of empty SELECT list (bug #8648)
 --
diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index 8bca1f5d55..b5931ee700 100644
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -466,6 +466,15 @@ explain (verbose, costs off)
   select x, x from
     (select (select random() where y=y) as x from (values(1),(2)) v(y)) ss;
 
+--
+-- Check we don't misoptimize a NOT IN where the subquery returns no rows.
+--
+create temp table notinouter (a int);
+create temp table notininner (b int not null);
+insert into notinouter values (null), (1);
+
+select * from notinouter where a not in (select b from notininner);
+
 --
 -- Check we behave sanely in corner case of empty SELECT list (bug #8648)
 --