Fix bug#11868 NOT NULL ref optimization in subquery used in update must be

disabled if ref is built with a key from the updated table

Problem was in add_not_null_conds() optimization function.
It contains following code:
JOIN_TAB *referred_tab= not_null_item->field->table->reginfo.join_tab;
...
add_cond_and_fix(&referred_tab->select_cond, notnull);
For UPDATE described in bug report referred_tab is 0 and dereferencing it
crashes the server.

2 files changed, 24 insertions, 0 deletions

diff --git a/mysql-test/r/update.result b/mysql-test/r/update.result
index d83952e118b..e35d4e29fe4 100644
--- a/mysql-test/r/update.result
+++ b/mysql-test/r/update.result
@@ -240,3 +240,14 @@ update t1, t2 set t1.a = t2.a where t2.b = t1.b;
 show warnings;
 Level	Code	Message
 drop table t1, t2;
+create table t1(f1 int, f2 int);
+create table t2(f3 int, f4 int);
+create index idx on t2(f3);
+insert into t1 values(1,0),(2,0);
+insert into t2 values(1,1),(2,2);
+UPDATE t1 SET t1.f2=(SELECT MAX(t2.f4) FROM t2 WHERE t2.f3=t1.f1);
+select * from t1;
+f1	f2
+1	1
+2	2
+drop table t1,t2;
diff --git a/mysql-test/t/update.test b/mysql-test/t/update.test
index 6a90fb95760..41f7d37e6d0 100644
--- a/mysql-test/t/update.test
+++ b/mysql-test/t/update.test
@@ -201,3 +201,16 @@ analyze table t1,t2;
 update t1, t2 set t1.a = t2.a where t2.b = t1.b;
 show warnings;
 drop table t1, t2;
+
+#
+# Bug #11868 Update with subquery with ref built with a key from the updated
+#            table crashes server
+#
+create table t1(f1 int, f2 int);
+create table t2(f3 int, f4 int);
+create index idx on t2(f3);
+insert into t1 values(1,0),(2,0);
+insert into t2 values(1,1),(2,2);
+UPDATE t1 SET t1.f2=(SELECT MAX(t2.f4) FROM t2 WHERE t2.f3=t1.f1);
+select * from t1;
+drop table t1,t2;