T-SQL行合并成列与列拆分成行

本文出处：http://www.cnblogs.com/wy123/p/6910468.html 

感觉最近sql也没少写，突然有一点生疏了，对于用的不是太频繁的一些操作，时间一久就容易生。

多行的某一个列合并成一个列

CREATE TABLE TestColumnMergeAndSplit
(
    Id int Identity(1,1),
    BusinessId int,
    BusinessValue varchar(20)
)
GO



INSERT INTO TestColumnMergeAndSplit
SELECT 1,'AAA'
UNION ALL
SELECT 1,'BBB'
UNION ALL
SELECT 1,'CCC'
UNION ALL
SELECT 2,'XXX'
UNION ALL
SELECT 2,'YYY'
UNION ALL
SELECT 2,'ZZZ'
GO

SELECT * FROM TestColumnMergeAndSplit
GO


SELECT  t1.BusinessId,
       STUFF
       (
            ( SELECT     ','+t2.BusinessValue 
              FROM      TestColumnMergeAndSplit t2
              WHERE     t2.BusinessId = t1.BusinessId
            FOR
              XML PATH('')
            ),
            1,1,''
        )
         AS ColNames
FROM   TestColumnMergeAndSplit t1
GROUP BY t1.BusinessId
GO

另外是一个相反的操作，借助上面合并之后的结果，将一个多个值的字符串列拆分开来，转换为多行，

用到的字符串拆分函数，比较常见

CREATE FUNCTION [dbo].[fn_SplitStringToTable] 
(
    @s     VARCHAR(max),
    @split VARCHAR(10)
)
RETURNS @re TABLE
        (
            Id INT IDENTITY(1,1),
            Value VARCHAR(100)
        )
AS
BEGIN

    IF @s IS NULL
        RETURN

    IF @split IS NULL
        RETURN

    IF(LEN(@split)<=0)
    BEGIN
        INSERT INTO @re VALUES (@s)
        RETURN
    END

    DECLARE @splitlen INT

    SET @splitlen=LEN(@split ) - 1
    WHILE CHARINDEX(@split, @s) > 0
    BEGIN
        INSERT @re VALUES(LEFT(@s, CHARINDEX(@split, @s) - 1))
        SET @s=STUFF(@s, 1, CHARINDEX(@split, @s) + @splitlen, '')
    END
    INSERT @re VALUES(@s)
    RETURN
END

测试脚本，没啥技术含量

CREATE TABLE TestColumnMergeAndSplit
(
    Id int Identity(1,1),
    BusinessId int,
    BusinessValue varchar(20)
)
GO

INSERT INTO TestColumnMergeAndSplit
SELECT 1,'AAA'
UNION ALL
SELECT 1,'BBB'
UNION ALL
SELECT 1,'CCC'
UNION ALL
SELECT 2,'XXX'
UNION ALL
SELECT 2,'YYY'
UNION ALL
SELECT 2,'ZZZ'
GO

SELECT * FROM TestColumnMergeAndSplit
GO
--合并多列为一列
SELECT  t1.BusinessId,
       STUFF
       (
            ( SELECT     ','+t2.BusinessValue 
              FROM      TestColumnMergeAndSplit t2
              WHERE     t2.BusinessId = t1.BusinessId
              FOR XML PATH('')
            ),
            1,1,''
        )
         AS ColString
FROM   TestColumnMergeAndSplit t1
GROUP BY t1.BusinessId
GO

SELECT * FROM TestColumnMergeAndSplit_BAK
GO

SELECT t1.BusinessId,t1.ColString,t2.Id,t2.Value 
FROM TestColumnMergeAndSplit_BAK t1
    CROSS APPLY dbo.fn_SplitStringToTable(ColString,',')t2 
GO