A fix (bug #10176: problem with varchar keys).

myisam/mi_key.c:
  A fix (bug #10176: problem with varchar keys).
  Should skip key pack length for 'old' too.

myisam/mi_key.c

@@ -242,7 +242,10 @@ uint _mi_pack_key(register MI_INFO *info, uint keynr, uchar *key, uchar *old,
       {
 	k_length-=length;
         if (keyseg->flag & (HA_VAR_LENGTH_PART | HA_BLOB_PART))
+        {
           k_length-=2;                                  /* Skip length */
+          old+= 2;
+        }
 	continue;					/* Found NULL */
       }
     }

mysql-test/include/varchar.inc

@@ -226,3 +226,13 @@ create table t1 (v varchar(65530), key(v(10)));
 insert into t1 values(repeat('a',65530));
 select length(v) from t1 where v=repeat('a',65530);
 drop table t1;
+
+#
+# Bug #9489: problem with hash indexes
+#
+
+create table t1(a int, b varchar(12), key ba(b, a));
+insert into t1 values (1, 'A'), (20, NULL);
+explain select * from t1 where a=20 and b is null;
+select * from t1 where a=20 and b is null;
+drop table t1;

mysql-test/r/bdb.result

@@ -1858,6 +1858,15 @@ select length(v) from t1 where v=repeat('a',65530);
 length(v)
 65530
 drop table t1;
+create table t1(a int, b varchar(12), key ba(b, a));
+insert into t1 values (1, 'A'), (20, NULL);
+explain select * from t1 where a=20 and b is null;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	ba	ba	20	const,const	1	Using where
+select * from t1 where a=20 and b is null;
+a	b
+20	NULL
+drop table t1;
 create table t1 (v varchar(65530), key(v));
 Warnings:
 Warning	1071	Specified key was too long; max key length is 255 bytes

mysql-test/r/innodb.result

@@ -2359,6 +2359,15 @@ select length(v) from t1 where v=repeat('a',65530);
 length(v)
 65530
 drop table t1;
+create table t1(a int, b varchar(12), key ba(b, a));
+insert into t1 values (1, 'A'), (20, NULL);
+explain select * from t1 where a=20 and b is null;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	ba	ba	20	const,const	1	Using where; Using index
+select * from t1 where a=20 and b is null;
+a	b
+20	NULL
+drop table t1;
 create table t1 (v varchar(65530), key(v));
 ERROR HY000: Can't create table './test/t1' (errno: 139)
 create table t1 (v varchar(65536));

mysql-test/r/myisam.result

@@ -1157,6 +1157,15 @@ select length(v) from t1 where v=repeat('a',65530);
 length(v)
 65530
 drop table t1;
+create table t1(a int, b varchar(12), key ba(b, a));
+insert into t1 values (1, 'A'), (20, NULL);
+explain select * from t1 where a=20 and b is null;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	ba	ba	20	const,const	1	Using where; Using index
+select * from t1 where a=20 and b is null;
+a	b
+20	NULL
+drop table t1;
 create table t1 (v varchar(65530), key(v));
 Warnings:
 Warning	1071	Specified key was too long; max key length is 1000 bytes