如何使用mysql在分層數據模式中創建此SELECT？

我已經使用分層數據模式來存儲數據庫中的產品。產品只有主要和子類別，這是我檢索完整產品樹時的結果。如何使用mysql在分層數據模式中創建此SELECT？

SELECT t1.name AS lev1, 
      t2.name as lev2, 
      t3.name as lev3, 
FROM categories AS t1 
    LEFT JOIN categories AS t2 
     ON t2.parent = t1.category_id 
    LEFT JOIN categories AS t3 
     ON t3.parent = t2.category_id 
WHERE t1.name = 'Products' 

+----------+----------------------+-------------------+ 
| lev1  | lev2     | lev3    | 
+----------+----------------------+-------------------+ 
| Products | Computers   | Laptops   | 
| Products | Computers   | Desktop Computers | 
| Products | Computers   | Tab PCs   | 
| Products | Computers   | CRT Monitors  | 
| Products | Computers   | LCD Monitors  | 
| Products | Computers   | LED Monitors  | 
| Products | Mobile Phones  | LG Phone   | 
| Products | Mobile Phones  | Anroid Phone  | 
| Products | Mobile Phones  | Windows Mobile | 
| Products | Mobile Phones  | iPad    | 
| Products | Mobile Phones  | Samsung Galaxy | 
| Products | Digital Cameras  | test    | 
| Products | Printers and Toners | NULL    | 
| Products | test     | abc    | 
| Products | test2    | NULL    | 
| Products | test3    | NULL    | 
| Products | Computer Accessaries | USB Cables  | 
| Products | Computer Accessaries | Network Cables | 
+----------+----------------------+-------------------+

我的問題是我需要選擇level2和level3類別ID以及此選擇查詢。

我想它是這樣的：

SELECT t1.name AS lev1, 
       t2.name as lev2, 
       t3.name as lev3, 
       t3.category_id 
FROM categories AS t1 
    LEFT JOIN categories AS t2 
     ON t2.parent = t1.category_id 
    LEFT JOIN categories AS t3 
     ON t3.parent = t2.category_id 
WHERE t1.name = 'Products'

但其只提供3級標識。喜歡這個。

+----------+----------------------+-------------------+-------------+ 
| lev1  | lev2     | lev3    | category_id | 
+----------+----------------------+-------------------+-------------+ 
| Products | Computers   | Laptops   |   3 | 
| Products | Computers   | Desktop Computers |   4 | 
| Products | Computers   | Tab PCs   |   5 | 
| Products | Computers   | CRT Monitors  |   6 | 
| Products | Computers   | LCD Monitors  |   7 | 
| Products | Computers   | LED Monitors  |   8 | 
| Products | Mobile Phones  | LG Phone   |   10 | 
| Products | Mobile Phones  | Anroid Phone  |   11 | 
| Products | Mobile Phones  | Windows Mobile |   12 | 
| Products | Mobile Phones  | iPad    |   13 | 
| Products | Mobile Phones  | Samsung Galaxy |   14 | 
| Products | Digital Cameras  | test    |   21 | 
| Products | Printers and Toners | NULL    |  NULL | 
| Products | test     | abc    |   20 | 
| Products | test2    | NULL    |  NULL | 
| Products | test3    | NULL    |  NULL | 
| Products | Computer Accessaries | USB Cables  |   23 | 
| Products | Computer Accessaries | Network Cables |   24 | 
+----------+----------------------+-------------------+-------------+

有人可以告訴我怎樣才能同時獲得level2和level3？

來源

2015-10-10 user3733831

你解決問題了嗎？ –

如果你有一樣，如果產品只有二級類別沒有3級分類的方法，你可以嘗試

SELECT t1.name AS lev1,t2.name as lev2, t3.name as lev3,COALESCE(t3.category_id, t2.category_id) FROM categories AS t1 
LEFT JOIN categories AS t2 ON t2.parent = t1.category_id 
LEFT JOIN categories AS t3 ON t3.parent = t2.category_id WHERE t1.name = 'Products'

它給你2級的類ID時，沒有任何3級類別

來源

2015-10-10 03:45:55

OP想要：「我怎樣才能同時獲得level2和level3？」不只一個 –

如果你需要單獨使用level2和level3，那麼使用't2.category_id，t3.category_id'而不是'COALESCE（t3.category_id，t2.category_id）'，這會在單個列中給出結果。你必須在代碼中檢查level3的空值 –

添加到您的領域這個t2.category_id,

SELECT t1.name AS lev1, 
       t2.name as lev2, 
       t2.category_id, 
       t3.name as lev3, 
       t3.category_id 
FROM categories AS t1 
    LEFT JOIN categories AS t2 
     ON t2.parent = t1.category_id 
    LEFT JOIN categories AS t3 
     ON t3.parent = t2.category_id 
WHERE t1.name = 'Products'

來源

2015-10-10 04:04:32

如何使用mysql在分層數據模式中創建此SELECT？

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