Proposed fix for #2093

it happens because of the LEFT JOINT optimization in add_key_part()
This optimization does exactly the same in JOIN and in WHERE conditions 
Not right.
I moved that optimization one level upper.


mysql-test/r/join_outer.result:
  appropriate test result
mysql-test/t/join_outer.test:
  test case
sql/sql_select.cc:
  optimizing of the left_join now only for WHERE conditions
  and for first table in list

2 files changed, 30 insertions, 0 deletions

diff --git a/mysql-test/r/join_outer.result b/mysql-test/r/join_outer.result
index debec01fbdc..ae4d99e6241 100644
--- a/mysql-test/r/join_outer.result
+++ b/mysql-test/r/join_outer.result
@@ -667,3 +667,20 @@ left outer join t2 using (f2)
 left outer join t3 using (f3);
 Unknown column 'test.t2.f3' in 'on clause'
 drop table t1,t2,t3;
+create table t1 (a1 int, a2 int);
+create table t2 (b1 int not null, b2 int);
+create table t3 (c1 int, c2 int);
+insert into t1 values (1,2), (2,2), (3,2);
+insert into t2 values (1,3), (2,3);
+insert into t3 values (2,4),        (3,4);
+select * from t1 left join t2  on  b1 = a1 left join t3  on  c1 = a1  and  b1 is null;
+a1	a2	b1	b2	c1	c2
+1	2	1	3	NULL	NULL
+2	2	2	3	NULL	NULL
+3	2	NULL	NULL	3	4
+explain select * from t1 left join t2  on  b1 = a1 left join t3  on  c1 = a1  and  b1 is null;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	ALL	NULL	NULL	NULL	NULL	3	
+t2	ALL	NULL	NULL	NULL	NULL	2	
+t3	ALL	NULL	NULL	NULL	NULL	2	
+drop table t1, t2, t3;
diff --git a/mysql-test/t/join_outer.test b/mysql-test/t/join_outer.test
index ee7d55d2a4e..bed4d4b033b 100644
--- a/mysql-test/t/join_outer.test
+++ b/mysql-test/t/join_outer.test
@@ -437,3 +437,16 @@ select * from t1
          left outer join t2 using (f2)
          left outer join t3 using (f3);
 drop table t1,t2,t3;
+
+create table t1 (a1 int, a2 int);
+create table t2 (b1 int not null, b2 int);
+create table t3 (c1 int, c2 int);
+
+insert into t1 values (1,2), (2,2), (3,2);
+insert into t2 values (1,3), (2,3);
+insert into t3 values (2,4),        (3,4);
+
+select * from t1 left join t2  on  b1 = a1 left join t3  on  c1 = a1  and  b1 is null;
+explain select * from t1 left join t2  on  b1 = a1 left join t3  on  c1 = a1  and  b1 is null;
+
+drop table t1, t2, t3;