如何在一列中返回多个值(T-SQL)？

Question

我有一个table UserAliases(UserId, Alias)每个用户有多个别名.我需要查询它并返回给定用户的所有别名,诀窍是将它们全部返回到一列中.

例:

UserId/Alias  
1/MrX  
1/MrY  
1/MrA  
2/Abc  
2/Xyz

我希望查询结果采用以下格式:

UserId/Alias  
1/ MrX, MrY, MrA  
2/ Abc, Xyz

谢谢.

我正在使用SQL Server 2005.

ps实际的T-SQL查询将不胜感激:)

Answer 1

您可以使用COALESCE的功能.

CREATE FUNCTION [dbo].[GetAliasesById]
(
    @userID int
)
RETURNS varchar(max)
AS
BEGIN
    declare @output varchar(max)
    select @output = COALESCE(@output + ', ', '') + alias
    from UserAliases
    where userid = @userID

    return @output
END

GO

SELECT UserID, dbo.GetAliasesByID(UserID)
FROM UserAliases
GROUP BY UserID

GO

Answer 2

嗯......我看到答案已被接受......但我认为你应该看到另一种解决方案:

/* EXAMPLE */
DECLARE @UserAliases TABLE(UserId INT , Alias VARCHAR(10))
INSERT INTO @UserAliases (UserId,Alias) SELECT 1,'MrX'
     UNION ALL SELECT 1,'MrY' UNION ALL SELECT 1,'MrA'
     UNION ALL SELECT 2,'Abc' UNION ALL SELECT 2,'Xyz'

/* QUERY */
;WITH tmp AS ( SELECT DISTINCT UserId FROM @UserAliases )
SELECT 
    LEFT(tmp.UserId, 10) +
    '/ ' +
    STUFF(
            (   SELECT ', '+Alias 
                FROM @UserAliases 
                WHERE UserId = tmp.UserId 
                FOR XML PATH('') 
            ) 
            , 1, 2, ''
        ) AS [UserId/Alias]
FROM tmp

/* -- OUTPUT
  UserId/Alias
  1/ MrX, MrY, MrA
  2/ Abc, Xyz    
*/