SQL - SUM() 上的 WHERE 条件

2022-01-09 00:00:00 sql sum conditional-statements mysql

是否可以这样做:

SELECT 
  `e`.*, 
  `rt`.`review_id`, 
  (SUM(vt.percent) / COUNT(vt.percent)) AS rating 
FROM `catalog_product_entity` AS `e` 
INNER JOIN `rating_option_vote` AS `vt`
  ON vt.review_id = e.review_id 
WHERE (rating >= '0') 
GROUP BY `vt`.`review_id`

我特别想在除法结果值上加上 where 条件

In particular I would like to put a where condition on the division result value

推荐答案

这可以通过 HAVING 子句来完成:

This can be accomplished with a HAVING clause:

SELECT e.*, rt.review_id, (SUM(vt.percent) / COUNT(vt.percent)) AS rating 
FROM catalog_product_entity AS e 
INNER JOIN rating_option_vote AS vt ON e.review_id = vt.review_id 
GROUP BY vt.review_id
HAVING (SUM(vt.percent) / COUNT(vt.percent)) >= 0
ORDER BY (SUM(vt.percent) / COUNT(vt.percent)) ASC

注意:添加了 ORDER BY 语句的放置位置

Note: Added where to put ORDER BY statement

查询优化器也不应该多次计算平均值，所以这里不应该担心.

The query optimizer should also not calculate the Average multiple times either, so that should not be a concern here.

正如@jagra 的回答中提到的，您应该能够使用 AVG() 而不是 SUM()/COUNT()

As was mentioned in @jagra's answer, you should be able to use AVG() instead of SUM() / COUNT()

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