SQL 有聚合函数吗？答案

【问题标题】：SQL Having aggregate function?SQL 有聚合函数吗？
【发布时间】：2016-08-15 06:22:12
【问题描述】：

我有学生和评估表。必须返回所有评分的重复次数，但没有 MIN 和 MAX 重复次数等级。

当我运行这个查询时：

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

我有这个结果，没关系，但是如何在没有 MIN 和 MAX 重复次数的情况下显示此查询。（在这种情况下为 6 - 120 和 10 - 4）

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

我用这种方式尝试了 HAVING，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。

【问题讨论】：

你用的是什么数据库？
MS SQL Server 2012

标签： sql sql-server max min having

【解决方案1】：

你不能像这样嵌套聚合函数。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 获得极值：

 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 关键字只使用一次。

【讨论】：

【解决方案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

【讨论】：

你应该给一个复选标记答案。我不在乎你是否给戈登答案。

【解决方案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)
)

这里我们使用了类似于子查询的公用表表达式的概念。

【讨论】：

酷！很高兴它有帮助。 :)

【解决方案4】：

我通过这种方式解决了这个问题，但 CTE 就是一个很好的例子。谢谢大家。

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)

【讨论】：