MDEV-28351 Assertion `this->file->children_attached' failed in ha_myisammrg::info

Reviewed-by: <vicentiu@mariadb.org>

mysql-test/main/information_schema_temp_table.result

@@ -200,3 +200,17 @@ show index in t;
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment	Index_comment	Ignored
 t	1	b	1	b	A	NULL	NULL	NULL	YES	BTREE			NO
 drop database mysqltest;
+#
+# MDEV-28351 Assertion `this->file->children_attached' failed in ha_myisammrg::info
+#
+use test;
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+insert into t1 values (1);
+CREATE TEMPORARY TABLE t2 (a INT) ENGINE=MERGE UNION=(t1);
+CREATE TABLE t3 (a INT) ENGINE=MERGE UNION=(t1);
+SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'test';
+TABLE_CATALOG	TABLE_SCHEMA	TABLE_NAME	TABLE_TYPE	ENGINE	VERSION	ROW_FORMAT	TABLE_ROWS	AVG_ROW_LENGTH	DATA_LENGTH	MAX_DATA_LENGTH	INDEX_LENGTH	DATA_FREE	AUTO_INCREMENT	CREATE_TIME	UPDATE_TIME	CHECK_TIME	TABLE_COLLATION	CHECKSUM	CREATE_OPTIONS	TABLE_COMMENT	MAX_INDEX_LENGTH	TEMPORARY
+def	test	tmp_innodb_in_test	TEMPORARY	InnoDB	10	Dynamic	0	0	X	X	X	X	NULL	X	X	NULL	latin1_swedish_ci	NULL			X	Y
+def	test	t3	BASE TABLE	MRG_MyISAM	10	Fixed	1	5	X	X	X	X	NULL	X	X	NULL	latin1_swedish_ci	NULL			X	N
+def	test	t1	BASE TABLE	MyISAM	10	Fixed	1	7	X	X	X	X	NULL	X	X	NULL	latin1_swedish_ci	NULL			X	N
+DROP TABLE t1,t2,t3;

mysql-test/main/information_schema_temp_table.test

@@ -195,3 +195,15 @@ show index in t;
 
 # Cleanup
 drop database mysqltest;
+
+--echo #
+--echo # MDEV-28351 Assertion `this->file->children_attached' failed in ha_myisammrg::info
+--echo #
+use test;
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+insert into t1 values (1);
+CREATE TEMPORARY TABLE t2 (a INT) ENGINE=MERGE UNION=(t1);
+CREATE TABLE t3 (a INT) ENGINE=MERGE UNION=(t1);
+--replace_column 10 X 11 X 12 X 13 X 15 X 16 X 22 X
+SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'test';
+DROP TABLE t1,t2,t3;

sql/sql_show.cc

@@ -5370,7 +5370,23 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
             }
             else /* SCH_TABLE */
             {
-              process_i_s_table_temporary_tables(thd, table, tmp_tbl);
+              if (tmp_tbl->file->ha_table_flags() & HA_CAN_MULTISTEP_MERGE)
+              {
+                /*
+                  MyISAM MERGE table. We have to to call open on it and its
+                  children
+                */
+                LEX_CSTRING table_name=
+                  { tmp_tbl->alias.ptr(), tmp_tbl->alias.length() };
+                if (fill_schema_table_by_open(thd, &tmp_mem_root, FALSE,
+                                              table, schema_table,
+                                              &tmp_tbl->s->db, &table_name,
+                                              &open_tables_state_backup,
+                                              0))
+                  goto err;
+              }
+              else
+                process_i_s_table_temporary_tables(thd, table, tmp_tbl);
             }
           }
         }