为什么MySQL 5.1.56中的查询失败?
以下查询在MySQL 5.1.56中失败:为什么MySQL 5.1.56中的查询失败?,mysql,Mysql,以下查询在MySQL 5.1.56中失败: 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.
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
错误是
#1054 - Unknown column 'products.product_id' in 'on clause'
没有用户表的修改不会失败:
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
在MySQL 5.0.67中,两个查询都没有失败。(我将数据库从5.0.67导出并导入5.1.56,因此结构应该相同。)
products表有一个product_id列,类型为int(10)。收藏夹表还有一个int(10)类型的product_id列。发生了什么事?从表中轻松交换订单:
FROM users, products LEFT JOIN
小心,您正在混合。与从表中交换命令一样简单:
FROM users, products LEFT JOIN
小心,您在混用。在5.1版的MySQL中,连接处理运算符的优先级已更改。对于从5.0升级的用户来说,这是一个常见的问题
在5.1版本的MySQL中,联接处理运算符优先级已更改。对于从5.0升级的用户来说,这是一个常见的问题
这是您的原始查询,重新格式化了一点,并添加了两个括号:
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
括号表示SQL解析器是如何解释查询的,并且添加的括号内没有products
表
混合使用旧样式和新样式(如中所示,因为SQL-92)是一个坏主意
使用:
=代码>连接将很慢(它实际上是笛卡尔乘积)。这是您的原始查询,重新格式化了一点,并添加了两个括号:
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
括号表示SQL解析器是如何解释查询的,并且添加的括号内没有products
表
混合使用旧样式和新样式(如中所示,因为SQL-92)是一个坏主意
使用:
=代码>连接速度会很慢(它实际上是笛卡尔积)。谢谢,这个解释很有帮助。看起来,如果我不混合连接符号,我可以在将来避免我原来的问题。一般来说,是的。在FROM子句中使用逗号分隔的表表达式列表应该知道符号的存在,以便在看到它时能够理解它。除非是因为过时的编码标准而被迫这样做,否则不应该编写这种类型的连接。默认情况下使用显式JOIN/ON表示法。谢谢,此解释非常有用。看起来,如果我不混合连接符号,我可以在将来避免我原来的问题。一般来说,是的。在FROM子句中使用逗号分隔的表表达式列表应该知道符号的存在,以便在看到它时能够理解它。除非是因为过时的编码标准而被迫这样做,否则不应该编写这种类型的连接。默认情况下使用显式JOIN/ON表示法。