BUG#9339 - Updating a column does not work if the table has a UTF-8 VARCHAR primary key

fixed my_charpos() call in Field_varstring::get_key_image

mysql-test/r/type_varchar.result

@@ -376,3 +376,10 @@ explain select * from t1 where v like 'S%' order by v;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	v	v	13	NULL	2	Using where; Using filesort
 drop table t1;
+create table t1 (pkcol varchar(16), othercol varchar(16), primary key (pkcol));
+insert into t1 values ('test', 'something');
+update t1 set othercol='somethingelse' where pkcol='test';
+select * from t1;
+pkcol	othercol
+test	somethingelse
+drop table t1;

mysql-test/t/type_varchar.test

@@ -97,3 +97,12 @@ explain select * from t1 where v like 'This is a test' order by v;
 explain select * from t1 where v='This is a test' order by v;
 explain select * from t1 where v like 'S%' order by v;
 drop table t1;
+
+#
+# bug#9339 - meaningless Field_varstring::get_key_image
+#
+create table t1 (pkcol varchar(16), othercol varchar(16), primary key (pkcol));
+insert into t1 values ('test', 'something');
+update t1 set othercol='somethingelse' where pkcol='test';
+select * from t1;
+drop table t1;

sql/field.cc

@@ -5725,12 +5725,12 @@ void Field_varstring::get_key_image(char *buff, uint length, imagetype type)
 {
   uint f_length=  length_bytes == 1 ? (uint) (uchar) *ptr : uint2korr(ptr);
   uint char_length= length / field_charset->mbmaxlen;
-  char_length= my_charpos(field_charset, ptr, ptr + length_bytes,
-                          char_length);
+  char *pos= ptr+length_bytes;
+  char_length= my_charpos(field_charset, pos, pos + f_length, char_length);
   set_if_smaller(f_length, char_length);
   /* Key is always stored with 2 bytes */
   int2store(buff,f_length);
-  memcpy(buff+HA_KEY_BLOB_LENGTH, ptr+length_bytes, f_length);
+  memcpy(buff+HA_KEY_BLOB_LENGTH, pos, f_length);
   if (f_length < length)
   {
     /*