fixed Field::eq() to work with CHAR(0) fields

.bzrignore

@@ -333,3 +333,5 @@ innobase/autom4te.cache/requests
 innobase/autom4te.cache/traces.0
 innobase/stamp-h1
 stamp-h1
+configure.lineno
+innobase/configure.lineno

mysql-test/r/delete.result

+bool	not_null	misc
+NULL	c	6
+NULL	d	7
+bool	not_null	misc

mysql-test/t/delete.test

@@ -35,3 +35,23 @@ create table t1 (a bigint not null, primary key (a,a,a,a,a,a,a,a,a,a));
 insert into t1 values (2),(4),(6),(8),(10),(12),(14),(16),(18),(20),(22),(24),(26),(23),(27);
 delete from t1 where a=27;
 drop table t1;
+
+#
+# CHAR(0) bug - not actually DELETE bug, but anyway...
+#
+
+CREATE TABLE t1 (
+  bool     char(0) default NULL,
+  not_null varchar(20) binary NOT NULL default '',
+  misc     integer not null,
+  PRIMARY KEY  (not_null)
+) TYPE=MyISAM;
+
+INSERT INTO t1 VALUES (NULL,'a',4), (NULL,'b',5), (NULL,'c',6), (NULL,'d',7);
+
+select * from t1 where misc > 5 and bool is null;
+delete   from t1 where misc > 5 and bool is null;
+select * from t1 where misc > 5 and bool is null;
+
+drop table t1;
+

sql/field.h

@@ -64,7 +64,7 @@ public:
   virtual String *val_str(String*,String *)=0;
   virtual Item_result result_type () const=0;
   virtual Item_result cmp_type () const { return result_type(); }
-  bool eq(Field *field) { return ptr == field->ptr; }
+  bool eq(Field *field) { return ptr == field->ptr && null_ptr == field->null_ptr; }
   virtual bool eq_def(Field *field);
   virtual uint32 pack_length() const { return (uint32) field_length; }
   virtual void reset(void) { bzero(ptr,pack_length()); }