Question

我正在开发一个商业评论系统。 business表是 -

id     category
1         1
2         1
3         1
4         2

review表是 -

id     bid     reviewer_point
1       1             4
2       1             3
3       2             4
4       2             5

我需要返回10过滤后评分最高的business ID category个（基于评分点平均值）业务。

到目前为止，我可以找到每项业务的平均评分。

SELECT business.category, bid, 
     COUNT(*) AS review_count, AVG(reviewer_point) AS average_points 
FROM reviews 
GROUP BY bid    
ORDER BY average_points DESC WHERE category = 1 LIMIT 10;

我无法使用WHERE条款。我怎样才能得到我的首选解决方案。提前致谢

Answer 1

mysql单个查询中的顺序是：

1st SELECT;
2nd FROM;
3rd WHERE;
4th GROUP BY;
5th HAVING;
6th ORDER BY;
7th LIMIT.

尝试将每个都放在一个断行线上。

Answer 2

WHERE子句必须在GROUP BY

之前

SELECT business.category, bid, 
     COUNT(*) AS review_count, AVG(reviewer_point) AS average_points 
FROM review
WHERE category = 1 
GROUP BY bid    
ORDER BY average_points DESC
LIMIT 10;

但是，由于business表尚未加入此查询，因此仍然无效。我会包含此内容，但没有明显的方法可以将business加入review。 review表格是否应该包含对business.id？

的引用的列

SQLFiddle here

祝你好运。

修改

通过OP在评论（下面）中提供的信息，修订后的查询变为

SELECT b.category, r.bid, 
     COUNT(*) AS review_count, AVG(reviewer_point) AS average_points 
FROM review r
INNER JOIN business b
  ON b.id = r.bid
WHERE b.category = 1 
GROUP BY r.bid, b.category
ORDER BY average_points DESC
LIMIT 10;

和the updated SQLFiddle can be found here

在mysql中加入表

2 个答案:

修改