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.

1 files changed, 13 insertions, 0 deletions

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;