MySQL WHERE子句和按avg()作为子查询排序

Question

虽然我可以在别名子查询上进行分组和排序，但我不能在where子句中使用该别名。我需要使用连接吗？

可行：

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子句中未知的列'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

- Mike

Answer 1

你可以使用HAVING子句代替WHERE子句来实现这一点。 语法

- Jason

Answer 2

我会使用join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)

这只是伪代码，我建议你仅限制所需的列数。

你可以使用类似以下的别名:

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

- Kevin Fisher