SQL Server模式SQL

Question

我有一张表列出了每个班级学生的成绩。 我想要的结果集看起来像：

BIO...B 
CHEM...C 

其中“B”和“C”是该类的模式。 我可以得到所有等级的方式，但不知道如何让每类模式

Answer 1

这里，像这样的SQL 2005/2008：

;WITH 
    Counts AS (
    SELECT ClassName, Grade, COUNT(*) AS GradeFreq 
    FROM Scores 
    GROUP BY ClassName, Grade 
    ) 
, Ranked AS (
    SELECT ClassName, Grade, GradeFreq 
    , Ranking = DENSE_RANK() OVER (PARTITION BY ClassName ORDER BY GradeFreq DESC) 
    FROM Counts 
    ) 
SELECT * FROM Ranked WHERE Ranking = 1 

或者只是：

;WITH Ranked AS (
    SELECT 
    ClassName, Grade 
    , GradeFreq = COUNT(*) 
    , Ranking = DENSE_RANK() OVER (PARTITION BY ClassName ORDER BY COUNT(*) DESC) 
    FROM Scores 
    GROUP BY ClassName, Grade 
) 
SELECT * FROM Ranked WHERE Ranking = 1 

Answer 2

你只需要GROUP BY ClassName

SELECT ClassName, MODE(Grade) FROM YourTable GROUP BY ClassName 

Answer 3

，如果您想要的模式，一个解决方案是在这里：

http://oreilly.com/catalog/transqlcook/chapter/ch08.html 
"Calculating a Mode" 

，如果你想在中间，看看在SQL Server此解决方案：

http://oreilly.com/catalog/transqlcook/chapter/ch08.html 
scroll to "Calculating a Median" 

其他解决方案获得中位数：

http://www.sqlmag.com/Files/09/49872/Listing_05.txt 
http://www.tek-tips.com/faqs.cfm?fid=4751 

Answer 4

使用GROUP BY子句。

SELECT className, ClassMode(className) 
FROM Grades 
GROUP BY className 

你的模式（）函数将不得不当然被创建，但它会像一个简单的函数：

CREATE FUNCTION ClassMode(@ClassName varchar(50)) 
RETURNS varchar(2) 
AS 
BEGIN 
    Declare @temp varchar(2) 

    SELECT @temp = TOP 1 Grade, COUNT(*) Grades as frequency 
    FROM Grades 
    WHERE ClassName = @ClassName 
    GROUP BY ClassName 
    ORDER BY frequency DESC 

    RETURN @temp 
END