Bug #21302: Result not properly sorted when using an ORDER BY on a second

             table in a join
 The optimizer removes redundant columns in ORDER BY. It is considering 
redundant every reference to const table column, e.g b in :
create table t1 (a int, b int, primary key(a)); 
select 1 from t1 order by b where a = 1

But it must not remove references to const table columns if the 
const table is an outer table because there still can be 2 values :
the const value and NULL. e.g.:
create table t1 (a int, b int, primary key(a));
select t2.b c from t1 left join t1 t2 on (t1.a = t2.a and t2.a = 5) 
  order by c;


mysql-test/r/join_outer.result:
  Bug #21302: Result not properly sorted when using an ORDER BY on a second 
              table in a join
   - don't remove columns of const tables in ORDER BY if the const table 
     is an outer table.
mysql-test/r/order_by.result:
  Bug #21302: Result not properly sorted when using an ORDER BY on a second 
              table in a join
   - test case
mysql-test/t/order_by.test:
  Bug #21302: Result not properly sorted when using an ORDER BY on a second 
              table in a join
   - test case
sql/sql_select.cc:
  Bug #21302: Result not properly sorted when using an ORDER BY on a second 
              table in a join
   - don't remove columns of const tables in ORDER BY if the const table 
     is an outer table.

1 files changed, 37 insertions, 0 deletions

diff --git a/mysql-test/r/order_by.result b/mysql-test/r/order_by.result
index a36935a583d..69a5509b68c 100644
--- a/mysql-test/r/order_by.result
+++ b/mysql-test/r/order_by.result
@@ -852,3 +852,40 @@ b	a
 20	1
 10	2
 DROP TABLE t1;
+CREATE TABLE t1 (a int, b int, PRIMARY KEY  (a));
+INSERT INTO t1 VALUES (1,1), (2,2), (3,3);
+explain SELECT t1.b as a, t2.b as c FROM 
+t1 LEFT JOIN t1 t2 ON (t1.a = t2.a AND t2.a = 2) 
+ORDER BY c;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	Using temporary; Using filesort
+1	SIMPLE	t2	const	PRIMARY	PRIMARY	4	const	1	
+SELECT t1.b as a, t2.b as c FROM 
+t1 LEFT JOIN t1 t2 ON (t1.a = t2.a AND t2.a = 2) 
+ORDER BY c;
+a	c
+1	NULL
+3	NULL
+2	2
+explain SELECT t1.b as a, t2.b as c FROM 
+t1 JOIN t1 t2 ON (t1.a = t2.a AND t2.a = 2)  
+ORDER BY c;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	const	PRIMARY	PRIMARY	4	const	1	
+1	SIMPLE	t2	const	PRIMARY	PRIMARY	4	const	1	
+CREATE TABLE t2 LIKE t1;
+INSERT INTO t2 SELECT * from t1;
+CREATE TABLE t3 LIKE t1;
+INSERT INTO t3 SELECT * from t1;
+CREATE TABLE t4 LIKE t1;
+INSERT INTO t4 SELECT * from t1;
+INSERT INTO t1 values (0,0),(4,4);
+SELECT t1.*,t2.* FROM t1 LEFT JOIN (t2, t3 LEFT JOIN t4 ON t3.a=t4.a)
+ON (t1.a=t2.a AND t1.b=t3.b) order by t2.b;
+a	b	a	b
+0	0	NULL	NULL
+4	4	NULL	NULL
+1	1	1	1
+2	2	2	2
+3	3	3	3
+DROP TABLE t1,t2,t3,t4;