Merge epotemkin@bk-internal.mysql.com:/home/bk/mysql-5.0

into sunlight.local:/local_work/16281-bug-5.0-mysql

sql/field.h

@@ -986,20 +986,23 @@ class Field_datetime :public Field_str {
 
 class Field_string :public Field_longstr {
 public:
+  bool can_alter_field_type;
   Field_string(char *ptr_arg, uint32 len_arg,uchar *null_ptr_arg,
 	       uchar null_bit_arg,
 	       enum utype unireg_check_arg, const char *field_name_arg,
 	       struct st_table *table_arg, CHARSET_INFO *cs)
     :Field_longstr(ptr_arg, len_arg, null_ptr_arg, null_bit_arg,
-                   unireg_check_arg, field_name_arg, table_arg, cs) {};
+                   unireg_check_arg, field_name_arg, table_arg, cs),
+     can_alter_field_type(1) {};
   Field_string(uint32 len_arg,bool maybe_null_arg, const char *field_name_arg,
                struct st_table *table_arg, CHARSET_INFO *cs)
     :Field_longstr((char*) 0, len_arg, maybe_null_arg ? (uchar*) "": 0, 0,
-                   NONE, field_name_arg, table_arg, cs) {};
+                   NONE, field_name_arg, table_arg, cs),
+     can_alter_field_type(1) {};
 
   enum_field_types type() const
   {
-    return ((orig_table &&
+    return ((can_alter_field_type && orig_table &&
              orig_table->s->db_create_options & HA_OPTION_PACK_RECORD &&
 	     field_length >= 4) &&
             orig_table->s->frm_version < FRM_VER_TRUE_VARCHAR ?

sql/sql_update.cc

@@ -1093,6 +1093,11 @@ multi_update::initialize_tables(JOIN *join)
     /* ok to be on stack as this is not referenced outside of this func */
     Field_string offset(table->file->ref_length, 0, "offset",
 			table, &my_charset_bin);
+    /*
+      The field will be converted to varstring when creating tmp table if
+      table to be updated was created by mysql 4.1. Deny this.
+    */
+    offset.can_alter_field_type= 0;
     if (!(ifield= new Item_field(((Field *) &offset))))
       DBUG_RETURN(1);
     ifield->maybe_null= 0;