MySQL:使用 ORDER BY 和 UNION

Question

请查看以下查询:

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)

这就是查询应该执行的操作:

• 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
• 每种产品可以有多个特价，因此只需选择优先级较高且持续时间较长的一个即可
• 从产品表中选择所有常规价格(仅选择在product_special 表中没有特价的产品)，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:

错误代码:1221。UNION 和 ORDER BY 的使用不正确

示例数据集:

Products

Specials

感谢任何帮助。

Answer 1

当您使用UNION时查询 LIMIT或ORDER BY对于每个单独的查询，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 )

您可以编写上述查询来避免此错误

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)
)