gistfile1.txt

mysql> EXPLAIN (SELECT Text FROM Strip_Text LEFT JOIN Strip_Panels ON Strip_Text.Parent_Table = "Panels" AND Strip_Text.Parent_ID = Strip_Panels.ID WHERE Strip_Panels.Strip_ID = 5) UNION ALL (SELECT DISTINCT Text FROM Strip_Text LEFT JOIN Strip_Panels ON Strip_Text.Parent_Table = "Scenes" AND Strip_Text.Parent_ID = Strip_Panels.Scene_ID WHERE Strip_Panels.Strip_ID = 5);
+----+--------------+--------------+------+------------------------+-----------+---------+------------------------------------------+------+------------------------------+
| id | select_type  | table        | type | possible_keys          | key       | key_len | ref                                      | rows | Extra                        |
+----+--------------+--------------+------+------------------------+-----------+---------+------------------------------------------+------+------------------------------+
| 1  | PRIMARY      | Strip_Panels | ref  | PRIMARY,Strip_ID       | Strip_ID  | 8       | const                                    | 4    | Using where                  |
| 1  | PRIMARY      | Strip_Text   | ref  | Parent_Table,Parent_ID | Parent_ID | 8       | Project_Doonesbury.Strip_Panels.ID       | 2    | Using where                  |
| 2  | UNION        | Strip_Panels | ref  | Strip_ID,Scene_ID      | Strip_ID  | 8       | const                                    | 4    | Using where; Using temporary |
| 2  | UNION        | Strip_Text   | ref  | Parent_Table,Parent_ID | Parent_ID | 8       | Project_Doonesbury.Strip_Panels.Scene_ID | 2    | Using where                  |
| NULL | UNION RESULT | <union1,2>   | ALL  | NULL                   | NULL      | NULL    | NULL                                     | NULL |                              |
+----+--------------+--------------+------+------------------------+-----------+---------+------------------------------------------+------+------------------------------+
5 rows in set (0.08 sec)

mysql> EXPLAIN SELECT DISTINCT Text FROM Strip_Text INNER JOIN Strip_Panels ON
(Strip_Text.Parent_Table = "Panels" AND Strip_Text.Parent_ID = Strip_Panels.ID)
OR (Strip_Text.Parent_Table = "Scenes" AND Strip_Text.Parent_ID = Strip_Panels.Scene_ID)
WHERE Strip_Panels.Strip_ID = 5;
+----+-------------+--------------+------+---------------------------+----------+---------+-------+-------+------------------------------------------------+
| id | select_type | table        | type | possible_keys             | key      | key_len | ref   | rows  | Extra                                          |
+----+-------------+--------------+------+---------------------------+----------+---------+-------+-------+------------------------------------------------+
| 1  | SIMPLE      | Strip_Panels | ref  | PRIMARY,Strip_ID,Scene_ID | Strip_ID | 8       | const | 4     | Using temporary                                |
| 1  | SIMPLE      | Strip_Text   | ALL  | Parent_ID                 | NULL     | NULL    | NULL  | 10098 | Range checked for each record (index map: 0x4) |
+----+-------------+--------------+------+---------------------------+----------+---------+-------+-------+------------------------------------------------+
2 rows in set (1.53 sec)