MySQL：使用 ORDER BY 和 UNION答案

【问题标题】：MySQL: Using ORDER BY and UNIONMySQL：使用 ORDER BY 和 UNION
【发布时间】：2014-05-30 02:36:20
【问题描述】：

请看下面的查询：

INSERT INTO product_filter (product_id,filter_id)
SELECT product_id,
(CASE WHEN price < 100 then 1
WHEN price >= 100 AND price < 500 then 2
WHEN price >= 500 AND price < 1000 then 3
WHEN price >= 1000 AND price < 1500 then 4
WHEN price >= 1500 AND price < 2000 then 5
WHEN price >= 2000 AND price < 2500 then 50
WHEN price >= 2500 AND price < 3000 then 6
ELSE 51 END) AS filter_id
FROM product_special
ORDER BY priority DESC, date_end DESC
LIMIT 1
UNION
SELECT product_id,
(CASE WHEN price < 100 then 1
WHEN price >= 100 AND price < 500 then 2
WHEN price >= 500 AND price < 1000 then 3
WHEN price >= 1000 AND price < 1500 then 4
WHEN price >= 1500 AND price < 2000 then 5
WHEN price >= 2000 AND price < 2500 then 50
WHEN price >= 2500 AND price < 3000 then 6
ELSE 51 END) AS filter_id
FROM product WHERE product_id not IN
(SELECT product_id FROM product_special)

这是查询应该做的：

从 product_special 表中选择所有特价，并根据价格将它们关联到不同的价格过滤器
每个产品都可以有多个特价，因此请选择优先级更高且持续时间更长的产品
从产品表中选择所有常规价格（仅那些在 product_special 表中没有特价的价格）并根据价格将它们关联到不同的价格过滤器

我收到的错误：

Error Code: 1221. Incorrect usage of UNION and ORDER BY

样本数据集：

Products

Specials

感谢任何帮助。

【问题讨论】：

标签： mysql e-commerce opencart mysql-workbench

【解决方案1】：

当您将UNION 查询与LIMIT 或ORDER BY 一起用于每个单独的查询时，您需要使用括号来组织查询，例如

(query 1 with limit order by ) 
 UNION 
(query 1 with limit order by )

你上面的查询可以写成避免这个错误

INSERT INTO product_filter (product_id,filter_id)
(
SELECT product_id,
(CASE WHEN price < 100 then 1
WHEN price >= 100 AND price < 500 then 2
WHEN price >= 500 AND price < 1000 then 3
WHEN price >= 1000 AND price < 1500 then 4
WHEN price >= 1500 AND price < 2000 then 5
WHEN price >= 2000 AND price < 2500 then 50
WHEN price >= 2500 AND price < 3000 then 6
ELSE 51 END) AS filter_id
FROM product_special
ORDER BY priority DESC, date_end DESC
LIMIT 1 )
UNION
(SELECT product_id,
(CASE WHEN price < 100 then 1
WHEN price >= 100 AND price < 500 then 2
WHEN price >= 500 AND price < 1000 then 3
WHEN price >= 1000 AND price < 1500 then 4
WHEN price >= 1500 AND price < 2000 then 5
WHEN price >= 2000 AND price < 2500 then 50
WHEN price >= 2500 AND price < 3000 then 6
ELSE 51 END) AS filter_id
FROM product WHERE product_id not IN
(SELECT product_id FROM product_special)
)

【讨论】：

谢谢，错误现在消失了。我只是不知道为什么查询没有做它应该做的事情。 Website
@farjam 你能否提供两个表的样本数据集而不是整个数据集只是一个样本，并且所需的结果集在插入后看起来像 product_filter 那样很容易看到发生了什么跨度>
@M Khalid Junaid，我将它们附加到问题中，谢谢。它们是 CSV 文件。

【解决方案2】：

您需要在第一个查询中为ORDER BY 和LIMIT 使用子查询。

类似这样的：

INSERT INTO product_filter (product_id,filter_id)
SELECT * FROM
(SELECT product_id,
(CASE WHEN price < 100 then 1
WHEN price >= 100 AND price < 500 then 2
WHEN price >= 500 AND price < 1000 then 3
WHEN price >= 1000 AND price < 1500 then 4
WHEN price >= 1500 AND price < 2000 then 5
WHEN price >= 2000 AND price < 2500 then 50
WHEN price >= 2500 AND price < 3000 then 6
ELSE 51 END) AS filter_id
FROM product_special
ORDER BY priority DESC, date_end DESC
LIMIT 1) a
UNION
SELECT product_id,
(CASE WHEN price < 100 then 1
WHEN price >= 100 AND price < 500 then 2
WHEN price >= 500 AND price < 1000 then 3
WHEN price >= 1000 AND price < 1500 then 4
WHEN price >= 1500 AND price < 2000 then 5
WHEN price >= 2000 AND price < 2500 then 50
WHEN price >= 2500 AND price < 3000 then 6
ELSE 51 END) AS filter_id
FROM product WHERE product_id not IN
(SELECT product_id FROM product_special)

【讨论】：

谢谢，错误现在消失了。我只是不知道为什么查询没有做它应该做的事情。 Example on my Website

【解决方案3】：

您应该使用圆括号来对单个查询使用 ORDER/LIMIT

例如

(SELECT * FROM table1 WHERE ... ORDER BY field1 LIMIT 0, 1)
UNION   
(SELECT * FROM table1 WHERE ...)

如果你在括号外使用 Order BY，它适用于 UNIONED 结果

【讨论】：