WHERE子句中的SQL查詢集合函數

Question

我對MSSQL語句有一些疑問。所以基本上這是我的SQL查詢：

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); 

我所試圖做的是子查詢裏，我每個用戶平均獲取最新組的列表。返回的例子數據（用戶名，avg_date）：

user1 10 
user2 20 
user3 20 

那之後，從外部查詢，我需要找到最小的從子查詢返回的平均日期。但是，通過這樣做，我得到和從外面的查詢錯誤消息，我只比較1列，從而子查詢返回2列。

的錯誤消息是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

然而，我的子查詢裏面我需要在GROUP BY每個用戶，所以我不能簡單地選擇平均。

任何想法如何解決這個問題？

在此先感謝。

Answer 1

試試這個

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) 
); 

另類：

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)); 

編輯爲SQL Server

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);