SQL Aggregate function that combines like CONCAT

Hey all,
I'm trying to find a way to query a database, using several GROUP BY's, but I need the IDENTITYCOL to be put in an aggregate function that will give me a string representation of each IDENTITYCOL value. Something in between a SUM and a CONCAT. So basically if I have records with IDENTITYCOL's 1, 3, 4 and 5, I'd like to be able to call THISFUNCTION(IDENTITYCOL) AS Expr1 and get Expr1 to be "1,3,4,5". Is there anything remotely like this? Thanks!

Try something like this:

declare @result varchar(8000)
set @result = ''
select @result = (case
when @result = '' then cast(id as varchar(16))
else @result + ',' + cast(id as varchar(16))
end)
from sysobjects
select @result

Thanks very much! I'm having trouble getting it to be more useful though. I want to accept 3 arguments: @table, @column, and @where. Table being the @table selected from, @column being the column, and @where being a condition. I'm getting 'Error 156: Incorrect syntax near the keyword 'return'"

You should use the "dynamic" SQL, like:

declare @cmd varchar(8000)
set @cmd = 'declare @result varchar(8000)
set @result = ''''
select @result = (case
when @result = '''' then cast(@column as varchar(16))
else @result + '','' + cast(@column as varchar(16))
end)
from [' + @table + '] where ' + @where
exec(@cmd)

But you can't use EXECUTE within a function. Why function, not stored procedure?