MySQL的地方由平均子句和排序（）作为一个子查询(MySQL where clause and o

虽然我可以通过一个别名的子查询组和秩序，我不能在where子句中使用别名。 我需要使用连接呢？

作品：

SELECT entries.*, 
    (SELECT avg(value) 
    FROM `ratings`
    WHERE ratings.entry_id = entries.id) as avg_rating
FROM `entries` 
ORDER BY avg_rating DESC

失败（“where子句中未知列‘AVG_RATING’”）：

SELECT entries.*, 
    (SELECT avg(value) 
    FROM `ratings` 
    WHERE ratings.entry_id = entries.id) as avg_rating 
FROM `entries` 
WHERE avg_rating < '4.5000' ORDER BY avg_rating DESC

Answer 1:

您可以用HAVING子句要做到这一点，而不是一个WHERE的

句法

Answer 2:

我会做一个连接和GROUPBY例如，

SELECT entries.*, AVG(value)
FROM entries INNER JOIN ratings ON entries.id = ratings.entry_id 
GROUP BY entries.*
HAVING AVG(value) < '4.5000' 
ORDER BY AVG(value)

只是伪代码，我也建议你限制的条目列，正是你需要的。

你也许能够逃脱的别名，如：

SELECT entries.*, AVG(value) as avg_value
FROM entries INNER JOIN ratings ON entries.id = ratings.entry_id 
GROUP BY entries.*
HAVING avg_value < '4.5000' 
ORDER BY avg_value

文章来源: MySQL where clause and ordering by avg() as a sub query