5.2 merge

mysql-test/r/merge.result

@@ -2368,6 +2368,13 @@ FLUSH TABLES;
 ERROR HY000: Can't reopen table: 'm1'
 UNLOCK TABLES;
 DROP TABLE t1, t2, t3, m1;
+create temporary table t1_temp(i int);
+create temporary table tm_temp_temp (i int) engine=merge union=(t1_temp) insert_method=last;
+alter table tm_temp_temp insert_method=first;
+check table tm_temp_temp;
+Table	Op	Msg_type	Msg_text
+test.tm_temp_temp	check	status	OK
+drop temporary table t1_temp, tm_temp_temp;
 End of 5.1 tests
 # 
 # MDEV-4277: Crash inside mi_killed_in_mariadb() with myisammrg

mysql-test/t/merge.test

@@ -1863,6 +1863,15 @@ FLUSH TABLES;
 UNLOCK TABLES;
 DROP TABLE t1, t2, t3, m1;
 
+#
+#  MDEV-5266 MySQL:57657 - Temporary MERGE table with temporary underlying is broken by ALTER
+#
+create temporary table t1_temp(i int);
+create temporary table tm_temp_temp (i int) engine=merge union=(t1_temp) insert_method=last;
+alter table tm_temp_temp insert_method=first;
+check table tm_temp_temp;
+drop temporary table t1_temp, tm_temp_temp;
+
 --echo End of 5.1 tests
 
 --echo # 

storage/myisammrg/ha_myisammrg.cc

@@ -1125,31 +1125,36 @@ void ha_myisammrg::update_create_info(HA_CREATE_INFO *create_info)
 
   if (!(create_info->used_fields & HA_CREATE_USED_UNION))
   {
-    MYRG_TABLE *open_table;
+    TABLE_LIST *child_table;
     THD *thd=current_thd;
 
     create_info->merge_list.next= &create_info->merge_list.first;
     create_info->merge_list.elements=0;
 
-    for (open_table=file->open_tables ;
-	 open_table != file->end_table ;
-	 open_table++)
+    if (table->child_l != NULL)
+    {
+      for (child_table= table->child_l;;
+           child_table= child_table->next_global)
       {
         TABLE_LIST *ptr;
-      LEX_STRING db, name;
-      LINT_INIT(db.str);
 
-      if (!(ptr = (TABLE_LIST *) thd->calloc(sizeof(TABLE_LIST))))
+        if (!(ptr= (TABLE_LIST *) thd->calloc(sizeof(TABLE_LIST))))
           goto err;
-      split_file_name(open_table->table->filename, &db, &name);
-      if (!(ptr->table_name= thd->strmake(name.str, name.length)))
+
+        if (!(ptr->table_name= thd->strmake(child_table->table_name,
+                                            child_table->table_name_length)))
           goto err;
-      if (db.length && !(ptr->db= thd->strmake(db.str, db.length)))
+        if (child_table->db && !(ptr->db= thd->strmake(child_table->db,
+                                   child_table->db_length)))
           goto err;
 
         create_info->merge_list.elements++;
-      (*create_info->merge_list.next) = ptr;
+        (*create_info->merge_list.next)= ptr;
         create_info->merge_list.next= &ptr->next_local;
+
+        if (&child_table->next_global == table->child_last_l)
+          break;
+      }
     }
     *create_info->merge_list.next=0;
   }