WHERE 子句中的 SQL 查询聚合函数

Question

我有一些关于 MSSQL 语句的问题。所以基本上这是我的 SQL 查询：

SELECT table1.col1, avg(datediff(dd, table2.date, table3.date)) as avg_date
INNER JOIN table2
INNER JOIN table3
WHERE avg_date <= ALL
(SELECT table1.col1, avg(datediff(dd, table2.date, table3.date)) as avg_date
INNER JOIN table2
INNER JOIN table3
GROUP BY table1.col1);

我想做的是在子查询中，我得到每个用户的平均日期组列表。返回的示例数据为 (userName, avg_date)：

user1  10
user2  20
user3  20

然后在那之后，从外面的查询中，我需要找到从子查询返回的平均日期的最小值。但是，通过这样做，我收到了来自外部查询的错误消息，我只比较 1 列，而子查询返回 2 列。

错误信息是An aggregate may not appear in the WHERE clause unless it is in a subquery contained in a HAVING clause or a select list, and the column being aggregated is an outer reference

但是，在我的子查询中，我需要每个用户的 GROUP BY，所以我不能简单地 SELECT avg。

任何想法如何解决这个问题？

提前致谢。

Answer 1

试试这个

SELECT table1.col1, avg(datediff(dd, table2.date, table3.date)) as avg_date
INNER JOIN table2
INNER JOIN table3
HAVING avg_date <= (SELECT avg_date from
(SELECT table1.col1, avg(datediff(dd, table2.date, table3.date)) as avg_date
INNER JOIN table2
INNER JOIN table3
GROUP BY table1.col1)
);

替代方案：

SELECT * FROM
(
    SELECT table1.col1, avg(datediff(dd, table2.date, table3.date)) as avg_date
    INNER JOIN table2
    INNER JOIN table3
) outer_table
WHERE avg_date <= ALL(SELECT avg_date from(SELECT table1.col1,avg(datediff(dd, table2.date, table3.date)) as avg_date
INNER JOIN table2
INNER JOIN table3
GROUP BY table1.col1));

为 SQL Server 编辑

SELECT * FROM
(
    SELECT table1.col1, avg(datediff(dd, table2.date, table3.date)) as avg_date
    INNER JOIN table2
    INNER JOIN table3
) outer_table
WHERE avg_date <= ALL(SELECT inner_table.avg_date from
(SELECT table1.col1,avg(datediff(dd, table2.date, table3.date)) as avg_date
INNER JOIN table2
INNER JOIN table3
GROUP BY table1.col1) inner_table);