MySQL 使用 WHERE AVG() 选择最后 10 行

Question

我正在尝试提取平均评分高于 4 的最后 10 行的列表。现在这是通过从第一个表中选择然后检查平均值是否高于 4 然后将其添加到变量中来完成的它什么也不做。这是一种可怕的方法，尤其是在超过 1000 行的情况下。

这是两个查询：

SELECT * FROM `CLMS_reviews` WHERE id = 465 ORDER BY date DESC

SELECT 
rc.name, rr.rating
FROM `CLMS_reviews_ratings` rr  
LEFT JOIN `CLMS_reviews_categories` rc ON rc.cat_id = rr.cat_id  AND rc.website_id = 465
WHERE rr.review_id = " . $row['id'] . "
GROUP BY rc.name

如何将其合并到一个查询中？我试过了，但对 GROUP BY 的使用无效：

SELECT 
rr.review_id
FROM `CLMS_reviews` r
LEFT JOIN `CLMS_reviews_ratings` rr ON rr.review_id = r.id
WHERE r.website_id = 465 AND AVG(rr.rating) > 4
GROUP BY rr.review_id LIMIT 10

解决方案如下：

SELECT review_id FROM `CLMS_reviews_ratings`
WHERE review_id IN ((SELECT id FROM `CLMS_reviews` WHERE website_id = 465))
GROUP BY review_id
HAVING avg(rating) > 4
LIMIT 10

Answer 1

无法测试，但也许可以：

SELECT rr.review_id
  FROM `CLMS_reviews` r
  LEFT JOIN `CLMS_reviews_ratings` rr ON rr.review_id = r.id
 WHERE r.website_id = 465
 GROUP BY rr.review_id
HAVING avg(rr.rating) > 4
 LIMIT 10;

如果您需要过滤聚合函数，HAVING 是您的朋友。

Answer 2

我认为您需要使用HAVING 语法。像这样：

SELECT 
rr.review_id
FROM `CLMS_reviews` r
LEFT JOIN `CLMS_reviews_ratings` rr ON rr.review_id = r.id
WHERE r.website_id = 465
GROUP BY rr.review_id 
HAVING AVG(rr.rating) > 4
LIMIT 10