爲什麼此查詢在MySQL 5.1.56中失敗？

Question

下面的查詢在MySQL 56年5月1日失效：

SELECT 
shop_id, products.product_id AS 
product_id, brand, title, price, image, image_width, image_height 

FROM products, users LEFT JOIN 

(
    SELECT fav5.product_id AS product_id, SUM(CASE 
    WHEN fav5.current = 1 AND fav5.closeted = 1 THEN 1 
    WHEN fav5.current = 1 AND fav5.closeted = 0 THEN -1 
    ELSE 0 
    END) AS favorites_count 
    FROM favorites fav5 
    GROUP BY fav5.product_id 

) AS fav6 ON products.product_id=fav6.product_id 
WHERE products.product_id= 46876 AND users.user_id!=products.product_id 

的錯誤是

#1054 - Unknown column 'products.product_id' in 'on clause' 

未經用戶表此修改不會失敗：

SELECT 
shop_id, products.product_id AS 
product_id, brand, title, price, image, image_width, image_height 

FROM products LEFT JOIN 

(
    SELECT fav5.product_id AS product_id, SUM(CASE 
    WHEN fav5.current = 1 AND fav5.closeted = 1 THEN 1 
    WHEN fav5.current = 1 AND fav5.closeted = 0 THEN -1 
    ELSE 0 
    END) AS favorites_count 
    FROM favorites fav5 
    GROUP BY fav5.product_id 

) AS fav6 ON products.product_id=fav6.product_id 
WHERE products.product_id= 46876 

無論查詢中失敗MySQL 5.0.67。 （我從5.0.67導出數據庫並導入到5.1.56中，因此結構應該是相同的。）

產品表的確有product_id列，類型爲int（10）。收藏夾表中還有一個int類型的product_id列（10）。到底是怎麼回事？

Answer 1

一樣方便從表調劑訂購：

FROM users, products LEFT JOIN 

要小心，你混合join notations。

Answer 2

在5.1的MySQL中，JOIN處理運算符優先級已更改。它是人們從5.0 MySQL LEFT JOIN after 5.0.12 changes - How to rewrite query

Answer 3

這是你的原始查詢升級一個共同的問題，重新格式化一點點，有兩個括號補充說：

SELECT shop_id, products.product_id AS 
     product_id, brand, title, price, image, image_width, image_height 
    FROM products, 
     ( -- Parenthesis added 
     users LEFT JOIN 
     (
      SELECT fav5.product_id AS product_id, SUM(CASE 
      WHEN fav5.current = 1 AND fav5.closeted = 1 THEN 1 
      WHEN fav5.current = 1 AND fav5.closeted = 0 THEN -1 
      ELSE 0 
      END) AS favorites_count 
      FROM favorites fav5 
      GROUP BY fav5.product_id 
     ) AS fav6 ON products.product_id=fav6.product_id 
    ) -- Parenthesis added 
WHERE products.product_id= 46876 AND users.user_id!=products.product_id 

括號中指明的SQL語法分析器是如何解釋的查詢，在添加的括號內沒有products表。

混合舊式和新式（如自SQL-92以來）樣式連接是一個壞主意。

用途：

SELECT shop_id, products.product_id AS 
     product_id, brand, title, price, image, image_width, image_height 
    FROM products JOIN users ON users.user_id != products.product_id 
    LEFT JOIN 
     (SELECT fav5.product_id AS product_id, 
       SUM(CASE WHEN fav5.current = 1 AND fav5.closeted = 1 THEN 1 
         WHEN fav5.current = 1 AND fav5.closeted = 0 THEN -1 
         ELSE 0 
        END) AS favorites_count 
      FROM favorites fav5 
     GROUP BY fav5.product_id 
     ) AS fav6 ON products.product_id=fav6.product_id 
WHERE products.product_id = 46876 

的!=聯接將是緩慢的（它實際上是一個笛卡爾乘積）。