Try This:

CREATE FUNCTION dbo.MyFunction

(@ID int)

returns varchar(2000)

as

begin

 declare @rtrn varchar(2000)

 declare @temp varchar(500)

 declare @rowcount int 

 set @temp = ''

 set @rowcount = 1

 set @rtrn = ''

 while(@rowcount > 0)

 begin

  select top 1 @temp = [Name]

  from MyTable

  where [id]...