2 
SELECT c.review, m.category, u.username, i.item, i.item_id, m.cat_id, COUNT(rv.review_id) totalCount
FROM reviews AS c
LEFT JOIN review_vote as rv
   ON c.review_id = rv.review_id
LEFT JOIN users AS u
   ON u.user_id = c.user_id 
LEFT JOIN items AS i
   ON i.item_id = c.item_id
LEFT JOIN master_cat AS m
   ON m.cat_id = i.cat_id
WHERE LENGTH(c.review) > 50 AND m.category = 'Movies' AND totalCount > 2
GROUP BY rv.review_id
ORDER BY RAND()
LIMIT 1

我收到此错误：

#1054 - Unknown column 'totalCount' in 'where clause'

我马上就选这个栏目，怎么不存在呢？

我正在尝试随机选择表中列出（或投票 2 次或更多次）的评论rv。另外我不确定我GROUP BY是否正确使用？

4

1 回答 1

4

对于聚合列（如count()），您必须使用HAVING子句对它们设置条件：

SELECT c.review, m.category, u.username, i.item, i.item_id, m.cat_id, COUNT(rv.review_id) totalCount
FROM reviews AS c
LEFT JOIN review_vote as rv
   ON c.review_id = rv.review_id
LEFT JOIN users AS u
   ON u.user_id = c.user_id 
LEFT JOIN items AS i
   ON i.item_id = c.item_id
LEFT JOIN master_cat AS m
   ON m.cat_id = i.cat_id
WHERE LENGTH(c.review) > 50 AND m.category = 'Movies'
GROUP BY rv.review_id
HAVING COUNT(rv.review_id) > 2 -- Added this line!
ORDER BY RAND()
LIMIT 1

某些数据库（包括 mysql）允许您使用列别名，例如HAVING totalCount > 2，但使用该表达式适用于所有数据库。即对于mysql（至少），您可以将其编码为：

....
GROUP BY rv.review_id
HAVING totalCouunt > 2
...

但它不能移植到所有其他数据库。

于 2013-05-18T22:51:49.520 回答