Automerge.

sql/sql_select.cc

@@ -9797,6 +9797,7 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
   table->in_use= thd;
   table->quick_keys.init();
   table->covering_keys.init();
+  table->merge_keys.init();
   table->keys_in_use_for_query.init();
 
   table->s= share;

sql/table.cc

@@ -1652,6 +1652,7 @@ int open_table_from_share(THD *thd, TABLE_SHARE *share, const char *alias,
     goto err;
   outparam->quick_keys.init();
   outparam->covering_keys.init();
+  outparam->merge_keys.init();
   outparam->keys_in_use_for_query.init();
 
   /* Allocate handler */