SQL Server模式SQL

Question

我有一張表列出了每個班級學生的成績。 我想要的結果集看起來像：

BIO...B 
CHEM...C 

其中「B」和「C」是該類的模式。 我可以得到所有等級的方式，但不知道如何讓每類模式

Answer 1

這裏，像這樣的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，一個解決方案是在這裏：

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

，如果你想在中間，看看在SQL Server此解決方案：

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

其他解決方案獲得中位數：

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（）函數將不得不當然被創建，但它會像一個簡單的函數：

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