For Example:

Number Value.....
1          AD
2          GD
2          DE
3          IF
4          OG
4          JD

The output I would like is:-

1         AD
2         GD,DE
3         IF
4         OG,JD

You can also resolve this problem using function.

Create Function Concat( @iNumber int )
RETURNS varchar(500)
AS
BEGIN 
   DECLARE @List varchar(500)
   SET @List = ''
   Select @List = @List + strValue + ',' from Testing
   Where Number = @iNumber
   RETURN LEFT(@List,LEN(@List)-1)
End

And use this function in SQL Query.

select Number, dbo.Concat(Number) from Testing Group By Number