找出只有那些沒有孩子ORDER BY父母和祖父母

Question

表名的ID：水平

+-----+-------------------+----------+ 
| id | name    | parentid | 
+-----+-------------------+----------+ 
| 1 | AIR CONDITIONER | 0  | 
| 2 | TV    | 0  | 
| 3 | SPLIT TYPE  | 1  | 
| 4 | WINDOWS TYPE  | 1  | 
| 5 | LCD    | 2  | 
| 6 | PLASMA   | 2  | 
| 7 | MUSIC PLAYER  | 0  | 
| 8 | AC 0.75 TON  | 3  | 
| 9 | AC 1 TON   | 3  | 
| 10 | WT 0.75 TON  | 4  | 
| 11 | WT 1 TON   | 4  | 
| 12 | LCD 32" UP  | 5  | 
| 13 | LCD 4" UP  | 5  | 
| 14 | PHOTO ALBUMS  | 0  | 
| 15 | STANDUP TYPE  | 1  | 
| 16 | CD PLAYERS  | 7  | 
| 17 | MP3 PLAYERS  | 7  | 
| 18 | CDS    | 0  | 
| 19 | BOOKS   | 0  | 
| 20 | PORTABLE TV  | 2  | 
+-----+-------------------+----------+ 

所以第一，我累找出所有沒有孩子的用下面的查詢的ID：

SELECT 
     t1.id, 
     t1.name AS name, 
     t2.id AS parentid, 
     t2.name AS parent_name, 
     t3.id AS grandparentid, 
     t3.name AS grandparent_name 
FROM level t1 
     LEFT JOIN level t2 ON t1.parentid=t2.id 
     LEFT JOIN level t3 ON t2.parentid=t3.id 
     WHERE t1.id NOT IN (SELECT parentid from level) 

，並得到以下結果

+-----+--------------+----------------+-------------------+ 
| id | name  | parent_name | grandparent_name | 
+-----+--------------+----------------+-------------------+ 
| 6 | PLASMA  | TV    | NULL    | 
| 8 | AC 0.75 TON | SPLIT TYPE  | AIR CONDITIONER | 
| 9 | AC 1 TON  | SPLIT TYPE  | AIR CONDITIONER | 
| 10 | WT 0.75 TON | WINDOWS TYPE | AIR CONDITIONER | 
| 11 | AC 1 TON  | WINDOWS TYPE | AIR CONDITIONER | 
| 12 | LCD 32" UP | LCD   | TV    | 
| 13 | LCD 42" UP | LCD   | TV    | 
| 14 | PHOTO ALBUM | NULL   | NULL    | 
| 15 | STANDUP TYPE | AIR CONDITIONER| NULL    | 
| 16 | CD PLAYERS | MUSIC PLAYER | NULL    | 
| 17 | MP3 PLAYERS | MUSIC PLAYER | NULL    | 
| 18 | CDS   | NULL   | NULL    | 
| 19 | BOOKS  | NULL   | NULL    | 
| 19 | BOOKS  | NULL   | NULL    | 
+-----+--------------+----------------+-------------------+ 

這隻能得到沒有子記錄的ID但我需要創建一個選項，選擇菜單這是對用戶更友好是這樣的：

我已經試過ORDER BY t2.parentid DESC，t1.prentid DESC卻沒有得到我想要

方式示例（您可以忽略此示例。只給一個想法是什麼，我需要實現）：

<option>Air Conditioner >> STANDUP TYPE</option> 
<option>Air Conditioner >> SPLIT TYPE >> AC 0.75 TON</option> 
<option>Air Conditioner >> SPLIT TYPE >> AC 1 TON</option> 
<option>Air Conditioner >> WINDOWS TYPE >> AC 0.75 TON</option> 
<option>Air Conditioner >> WINDOWS TYPE >> AC 1 TON</option> 
<option>BOOKS</option> 
<option>CDS</option> 
<option>MUSIC PLAYERS >> MP3 PLAYERS</option> 
<option>MUSIC PLAYERS >> CDS PLAYERS</option> 
<option>PHOTO ALBUM</option> 
<option>TV >> LCD >> LCD 32" UP</option> 
<option>TV >> LCD >> LCD 42" UP</option> 
<option>TV >> PLASMA</option> 
<option>TV >> PORTABLE TV</option> 

所以我需要找出一個不同的查詢：

的處置RESULT

+-----+-------------------+------------------+--------------+ 
| id | grandparent_name | parent_name  | name  | 
+-----+-------------------+------------------+--------------+ 
| 15 | NULL    | AIR CONDITIONER | STANDUP TYPE | 
| 8 | AIR CONDITIONER | SPLIT TYPE  | AC 0.75 TON | 
| 9 | AIR CONDITIONER | SPLIT TYPE  | AC 1 TON  | 
| 10 | AIR CONDITIONER | WINDOWS TYPE  | WT 0.75 TON | 
| 11 | AIR CONDITIONER | WINDOWS TYPE  | AC 1 TON  | 
| 19 | NULL    | NULL    | BOOKS  | 
| 18 | NULL    | NULL    | CDS   | 
| 16 | NULL    | MUSIC PLAYERS | CD PLAYERS | 
| 17 | NULL    | MUSIC PLAYERS | MP3 PLAYERS | 
| 14 | NULL    | NULL    | PHOTO ALBUM | 
| 12 | TV    | LCD    | LCD 32" UP | 
| 13 | TV    | LCD    | LCD 42" UP | 
| 6 | NULL    | TV    | PLASMA  | 
| 20 | NULL    | TV    | PORTABLE TV | 
+-----+-------------------+------------------+--------------+ 

這是可以實現的？ 我可以使用CASE何時以及如何？

或者我必須使用PHP重新排序結果？

THX

Answer 1

這是稍有不同的結果比你想要的，但我覺得沒戲，你真正想要的：

SELECT (CASE WHEN l3.id IS NOT NULL THEN l3.id WHEN l2.id IS NOT NULL THEN l2.id ELSE l1.id END) as last_level_id, l1.name, l2.name, l3.name 
FROM level l1 
LEFT JOIN level l2 on l2.parentid = l1.id 
LEFT JOIN level l3 on l3.parentid = l2.id 
WHERE l1.parentid = 0 
ORDER BY l1.id, l2.id, l3.id