SqlServer行转列

本是古典何须时尚 2023-06-15 09:49 90阅读 0赞

## SQL Server行转列、不确定列的行转列 ##

## 本文使用的方法： ##

## **1、用Case When** ##

## **2、PIVOT函数** ##

首先，模拟一张表：

CREATE TABLE TempSubjectResult
    (
    StudentName NVARCHAR(50) NOT NULL,
    StudentSubject NVARCHAR(50) NOT NULL,
    StudentGrade DECIMAL(4,1) NOT NULL
    )
    INSERT INTO TempSubjectResult(StudentName,StudentSubject,StudentGrade) VALUES ('小姚','语文','80')
    INSERT INTO TempSubjectResult(StudentName,StudentSubject,StudentGrade) VALUES ('小姚','数学','70')
    INSERT INTO TempSubjectResult(StudentName,StudentSubject,StudentGrade) VALUES ('小姚','英语','60')
    INSERT INTO TempSubjectResult(StudentName,StudentSubject,StudentGrade) VALUES ('小明','语文','90')
    INSERT INTO TempSubjectResult(StudentName,StudentSubject,StudentGrade) VALUES ('小明','数学','95')
    INSERT INTO TempSubjectResult(StudentName,StudentSubject,StudentGrade) VALUES ('小明','英语','98')
    
    SELECT * FROM TempSubjectResult

表数据为：

![format_png][]

## \-----------------------------------------------------------------------------普通版：转置的列确定----------------------------------------------------------------------------- ##

## 方法一：Case When ##

-- 1 Case When普通版
    SELECT StudentName 学生名,
           MAX(CASE WHEN StudentSubject='语文' THEN StudentGrade END) 语文,
           MAX(CASE WHEN StudentSubject='数学' THEN StudentGrade END) 数学,
           MAX(CASE WHEN StudentSubject='英语' THEN StudentGrade END) 英语
      FROM TempSubjectResult
     GROUP BY StudentName

![format_png 1][]

## 方法二：PIVOT函数 ##

SELECT * 
      FROM TempSubjectResult 
      PIVOT(MAX(StudentGrade) FOR StudentSubject IN([语文],[数学],[英语])) T

![format_png 2][]

以上为知道学科有“语文、数学、英语”，如果不确定科目呢？

此时可以用动态SQL查询，请看进阶版

## \-----------------------------------------------------------------------------升级版：转置的列不确定----------------------------------------------------------------------------- ##

## 方法三、 Case When升级版 动态SQL ##

-- Case When升级版 动态SQL
    DECLARE @SqlText NVARCHAR(4000)='SELECT StudentName ''学生名'', ' -- SQL头部分 SELECT
    SELECT @SqlText=@SqlText+' MAX(CASE WHEN StudentSubject='''+StudentSubject+''' THEN StudentGrade END) '''+StudentSubject +''',' FROM (SELECT DISTINCT StudentSubject FROM TempSubjectResult) T -- 拼接CASE WHEN 
    SELECT @SqlText= LEFT(@SqlText,LEN(@SqlText)-1)+' FROM #TempSubjectResult GROUP BY StudentName' -- 拼接 FROM后面部分
    PRINT @SqlText
    EXEC (@SqlText)

![format_png 3][]

## 方法四、PIVOT升级版 动态SQL ##

-- PIVOT升级版 动态SQL
    DECLARE @SqlSubject NVARCHAR(4000)
    SELECT @SqlSubject= STUFF((SELECT '],[' + T.StudentSubject FROM (SELECT DISTINCT StudentSubject FROM TempSubjectResult) T  FOR XML PATH('')),1,2,'')+']' -- 获取PIVOT科目
    DECLARE @SqlPIVOT NVARCHAR(4000)='SELECT * FROM #TempSubjectResult PIVOT(MAX(StudentGrade) FOR StudentSubject IN('+@SqlSubject+')) T' -- 拼接PIVOT
    PRINT @SqlPIVOT
    EXEC (@SqlPIVOT)

![format_png 4][]

### 以下情况推荐使用动态转换： ###

### 1、需要转置的列不确定，比如转置月的天数，月份的天数有28.29.30.31天，不确定   2、需要转置的列非常多时候，不方便一个个写 ###

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