Bug #18895: BIT values cause joins to fail

The Field::eq() considered instances of Field_bit that differ only in 
bit_ptr/bit_ofs equal. This caused equality conditions optimization 
(build_equal_items_for_cond()) to make bad field substitutions that result
in wrong predicates. 
Field_bit requires an overloaded eq() function that checks the bit_ptr/bit_ofs
in addition to Field::eq().


mysql-test/r/select.result:
  Bug #18895: BIT values cause joins to fail
  
  - test case
mysql-test/t/select.test:
  Bug #18895: BIT values cause joins to fail
  
  - test case
sql/field.h:
  Bug #18895: BIT values cause joins to fail
  
  - eq() method overloaded for Field_bit

mysql-test/r/select.result

@@ -3359,3 +3359,23 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	PRIMARY,b	b	5	NULL	3	Using where
 1	SIMPLE	t2	ref	c	c	5	test.t1.a	2	Using where
 DROP TABLE t1, t2;
+create table t1 (
+a int unsigned    not null auto_increment primary key,
+b bit             not null,
+c bit             not null
+);
+create table t2 (
+a int unsigned    not null auto_increment primary key,
+b bit             not null,
+c int unsigned    not null,
+d varchar(50)
+);
+insert into t1 (b,c) values (0,1), (0,1);
+insert into t2 (b,c) values (0,1);
+select t1.a, t1.b + 0, t1.c + 0, t2.a, t2.b + 0, t2.c, t2.d
+from t1 left outer join t2 on t1.a = t2.c and t2.b <> 1
+where t1.b <> 1 order by t1.a;
+a	t1.b + 0	t1.c + 0	a	t2.b + 0	c	d
+1	0	1	1	0	1	NULL
+2	0	1	NULL	NULL	NULL	NULL
+drop table t1,t2;

mysql-test/t/select.test

@@ -2840,3 +2840,29 @@ EXPLAIN
 SELECT a, c, d, f FROM t1,t2 WHERE a=c AND b BETWEEN 4 AND 6 AND a > 0;
 
 DROP TABLE t1, t2;
+
+#
+# Bug #18895: BIT values cause joins to fail
+#
+create table t1 (
+    a int unsigned    not null auto_increment primary key,
+    b bit             not null,
+    c bit             not null
+);
+
+create table t2 (
+    a int unsigned    not null auto_increment primary key,
+    b bit             not null,
+    c int unsigned    not null,
+    d varchar(50)
+);
+
+insert into t1 (b,c) values (0,1), (0,1);
+insert into t2 (b,c) values (0,1);
+
+-- Row 1 should succeed.  Row 2 should fail.  Both fail.
+select t1.a, t1.b + 0, t1.c + 0, t2.a, t2.b + 0, t2.c, t2.d
+from t1 left outer join t2 on t1.a = t2.c and t2.b <> 1
+where t1.b <> 1 order by t1.a;
+
+drop table t1,t2;

sql/field.h

@@ -124,7 +124,7 @@ class Field
   static bool type_can_have_key_part(enum_field_types);
   static enum_field_types field_type_merge(enum_field_types, enum_field_types);
   static Item_result result_merge_type(enum_field_types);
-  bool eq(Field *field)
+  virtual bool eq(Field *field)
   {
     return (ptr == field->ptr && null_ptr == field->null_ptr &&
             null_bit == field->null_bit);
@@ -1358,6 +1358,13 @@ class Field_bit :public Field {
     bit_ptr= bit_ptr_arg;
     bit_ofs= bit_ofs_arg;
   }
+  bool eq(Field *field)
+  {
+    return (Field::eq(field) &&
+            field->type() == type() &&
+            bit_ptr == ((Field_bit *)field)->bit_ptr &&
+            bit_ofs == ((Field_bit *)field)->bit_ofs);
+  }
 };