SQL Server行转列、不确定列的行转列

佚名 6年前 (2019-05-10) 随笔 1904人围观抢沙发百度已收录

本文使用的方法：

1、用Case When

2、PIVOT函数

首先，模拟一张表：

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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：

-----------------------------------------------------------------------------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

方法二：PIVOT函数

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

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)

方法四、PIVOT升级版动态SQL

DECLARE @SqlSubject NVARCHAR(4000)
SELECT @SqlSubject= STUFF((SELECT ','+'['+StudentSubject+']' FROM (SELECT DISTINCT StudentSubject FROM #TempSubjectResult) T  FOR XML PATH('')),1,1,'') -- 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)

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

附：完整代码

-- 创建模拟数据
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

-- 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

-- 2 PIVOT普通版
SELECT * FROM #TempSubjectResult PIVOT(MAX(StudentGrade) FOR StudentSubject IN([语文],[数学],[英语])) T

-- 3 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)

-- 4 PIVOT升级版 动态SQL
DECLARE @SqlSubject NVARCHAR(4000)
SELECT @SqlSubject= STUFF((SELECT ','+'['+StudentSubject+']' FROM (SELECT DISTINCT StudentSubject FROM #TempSubjectResult) T  FOR XML PATH('')),1,1,'') -- 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)
DROP TABLE #TempSubjectResult