How to return multiple values in one column using T-SQL

Question

I have a table UserAliases (UserId, Alias) with multiple aliases per user. I need to query it and return all aliases for a given user, the trick is to return them all in one column.

Example:

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

I want the query result in the following format:

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

I'm using SQL Server 2005.

Answer 1

You can use a function with COALESCE.

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