SQL - 聚合可能不会出现在 WHERE 子句中，除非它位于 HAVING 子句中包含的子查询中

Posted 2023-02-16

【中文标题】SQL - 聚合可能不会出现在 WHERE 子句中，除非它位于 HAVING 子句中包含的子查询中

【英文标题】：SQL - An aggregate may not appear in the WHERE clause unless it is in a subquery contained in a HAVING clause

【发布时间】：2021-04-05 17:06:00

【问题描述】：

如果您看到下图，我只想查看平均收入高于总体平均水平的那些类别。

我正在使用的查询如下。最后一行导致了问题。

WITH cte_avg AS (
    SELECT P.prod_cat, Avg_revenue = AVG(CAST(T.total_amt AS NUMERIC))
    FROM [dbo].[Transactions] AS T
    LEFT JOIN [dbo].[prod_cat_info] AS P ON T.prod_cat_code=P.prod_cat_code
    GROUP BY P.prod_cat
)
SELECT prod_cat, Avg_revenue
FROM cte_avg
WHERE Avg_revenue > AVG(Avg_revenue)

我得到的错误是：

聚合可能不会出现在 WHERE 子句中，除非它出现在 HAVING 子句或选择列表中包含的子查询中，并且被聚合的列是外部引用。

请告诉我如何解决这个问题。谢谢！

【问题讨论】：

这能回答你的问题吗？ An aggregate may not appear in the WHERE clause unless it is in a subquery

【参考方案1】：

我认为您要编写的查询类似于：

select p.prod_cat, t.avg_total_amount
from (
    select prod_cat_code, avg(total_amount) as avg_total_amount
    from transactions
    group by prod_cat_code
    having avg(total_amount) > (select avg(total_amount) from transactions)
) t
inner join prod_cat_info p on p.prod_cat_code = t.prod_cat_code

子查询按类别聚合交易，计算平均值，并将其与整体交易平均值进行比较。然后我们只需将类别表与连接一起带入。

【参考方案2】：

我建议使用窗口函数。目前尚不清楚您所说的“平均总收入”是什么意思。如果您指的是产品总收入的平均值，那么：

SELECT *
FROM (SELECT P.prod_cat, SUM(total_amount) as total_revenue,
             AVG(SUM(total_amount)) OVER () as avg_total_revenue
      FROM [dbo].[Transactions] T JOIN
           [dbo].[prod_cat_info] P
            ON T.prod_cat_code=P.prod_cat_code
      GROUP BY P.prod_cat
     ) c
WHERE total_revenue > avg_total_revenue;

如果您指的是产品平均值与总体平均值相比：

SELECT *
FROM (SELECT P.prod_cat, AVG(total_amount) as avg_revenue,
             SUM(SUM(total_amount)) OVER () / SUM(COUNT(*)) as avg_total_revenue
      FROM [dbo].[Transactions] T JOIN
           [dbo].[prod_cat_info] P
            ON T.prod_cat_code=P.prod_cat_code
      GROUP BY P.prod_cat
     ) c
WHERE avg_revenue > avg_total_revenue

【参考方案3】：

以下查询解决了我的问题。

WITH cte_avg AS (SELECT P.prod_cat, Avg_revenue = AVG(CAST(T.total_amt AS NUMERIC))
    FROM [dbo].[Transactions] AS T
    LEFT JOIN [dbo].[prod_cat_info] AS P ON T.prod_cat_code=P.prod_cat_code
    GROUP BY P.prod_cat)
    SELECT prod_cat, Avg_revenue
    FROM cte_avg
    WHERE Avg_revenue>(SELECT AVG(Avg_revenue) FROM cte_avg)