SQL Server模式SQL

Question

我有一个表，列出了每个班级的学生成绩。我想要一个如下所示的结果集：

BIO...B
CHEM...C

其中"B“和"C”是类的模式。我可以获得所有年级的模式，但不确定如何获得每个班级的模式

Answer 1

下面是SQL 2005/2008中类似的内容：

;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

或者仅仅是：

;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

使用GROUP BY子句。

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

当然，您必须创建Mode()函数，但它将是一个简单的函数，如：

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

Answer 3

你只需要GROUP BY ClassName

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