Question

我有学生和评估表。有必要返回所有评级的重复次数，但没有MIN和MAX重复次数等级。

当我跑这个查询时：

SELECT 
     [Grade],
     COUNT([Grade]) AS [Number of repetitions]
     FROM [Test].[dbo].[Evaluation]
     GROUP BY Grade

我有这个结果，没关系，但如何用MIN和MAX重复次数显示这个查询。（在这种情况下6 - 120和10 - 4）

Grade    Number of repetitions
 6              120
 7              35
 8              93
 9              25
10              4

我尝试过以这种方式，但它不起作用。这是SQL中的消息：“无法对包含聚合或子查询的表达式执行聚合函数”

SELECT 
     [Grade],
     COUNT([Grade]) AS [Number of repetitions]
     FROM [Test].[dbo].[Evaluation]
     GROUP BY Grade 
     HAVING COUNT([Grade) > (SELECT MIN(COUNT([Grade])) FROM [Test][dbo].[Evaluation] GROUP BY Grade) 
     AND 
     HAVING COUNT([Grade) < (SELECT MAX(COUNT([Grade])) FROM [Test][dbo].[Evaluation] GROUP BY Grade)

非常感谢。

Answer 1

您不能嵌套这样的聚合函数。您可以使用许多方法来解决此问题。在您的情况下，您可以使用TOP和ORDER BY：

获取极值

 HAVING COUNT([Grade) > (SELECT TOP 1 COUNT([Grade]) FROM [Test].[dbo].[Evaluation] GROUP BY Grade ORDER BY COUNT([Grade]) ASC ) AND
        COUNT([Grade) < (SELECT TOP 1 COUNT([Grade]) FROM [Test].[dbo].[Evaluation] GROUP BY Grade ORDER BY COUNT([Grade]) DESC)

此外，HAVING关键字仅使用一次。

Answer 2

select TT.* 
FROM ( SELECT [Grade] 
            , COUNT([Grade]) AS [Number of repetitions]
            , ROW_NUMBER OVER (ORDER BY COUNT([Grade]) desc) rnD 
            , ROW_NUMBER OVER (ORDER BY COUNT([Grade]) asc)  rnA
         FROM [Test].[dbo].[Evaluation]
        GROUP BY Grade 
     ) TT
WHERE  TT.rnD <> 1 AND TT.rnA <> 1

Answer 3

WITH Fact As
(
SELECT 
     [Grade],
     COUNT([Grade]) AS [Number of repetitions]
     FROM [Test].[dbo].[Evaluation]
     GROUP BY Grade
)

SELECT Grade, [Number of repetitions] FROM Fact 
WHERE 
[Number of repetitions] NOT IN
(
(SELECT MAX([Number of repetitions]) FROM Fact), 
(SELECT MIN([Number of repetitions]) FROM Fact)
)

这里我们使用公共表表达式的概念，它类似于子查询。

Answer 4

我通过这种方式解决了这个问题，但是CTE就是很好的例子。谢谢大家。

cmake

SQL有聚合函数吗？

4 个答案: