Fix for BUG#8711: "<=>" may have true value for NULL arguments, so make

Item_func_equal::not_null_tables() always return 0.

mysql-test/r/join_outer.result

@@ -684,3 +684,23 @@ 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;
+create table t1 (
+a int(11),
+b char(10),
+key (a)
+);
+insert into t1 (a) values (1),(2),(3),(4);
+create table t2 (a int);
+select * from t1 left join t2 on t1.a=t2.a where not (t2.a <=> t1.a);
+a	b	a
+1	NULL	NULL
+2	NULL	NULL
+3	NULL	NULL
+4	NULL	NULL
+select * from t1 left join t2 on t1.a=t2.a having not (t2.a <=> t1.a);
+a	b	a
+1	NULL	NULL
+2	NULL	NULL
+3	NULL	NULL
+4	NULL	NULL
+drop table t1,t2;

mysql-test/t/join_outer.test

@@ -450,3 +450,16 @@ select * from t1 left join t2  on  b1 = a1 left join t3  on  c1 = a1  and  b1 is
 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;
+
+# Test for BUG#8711 '<=>' was considered to be a NULL-rejecting predicate.
+create table t1 (
+  a int(11),
+  b char(10),
+  key (a)
+);
+insert into t1 (a) values (1),(2),(3),(4);
+create table t2 (a int);
+
+select * from t1 left join t2 on t1.a=t2.a where not (t2.a <=> t1.a);
+select * from t1 left join t2 on t1.a=t2.a having not (t2.a <=> t1.a);
+drop table t1,t2;

sql/item_cmpfunc.h

@@ -78,6 +78,7 @@ public:
   Item_func_equal(Item *a,Item *b) :Item_bool_func2(a,b) { };
   longlong val_int();
   void fix_length_and_dec();
+  table_map not_null_tables() const { return 0; }
   enum Functype functype() const { return EQUAL_FUNC; }
   enum Functype rev_functype() const { return EQUAL_FUNC; }
   cond_result eq_cmp_result() const { return COND_TRUE; }