CREATE FUNCTION fn_format_number (@int_value int ) returns varchar(20)
AS
BEGIN
	DECLARE @is_negative BIT
	SELECT @is_negative = CASE WHEN @int_value<0 THEN 1 ELSE 0 END

	IF @is_negative = 1
		SET @int_value = -1*@int_value

	DECLARE @return_value VARCHAR(20)
	SET @return_value = CONVERT(VARCHAR, ISNULL(@int_value, 0))

	DECLARE @before VARCHAR(20), @after VARCHAR(20)

	SET @before = @return_value
	SET @after=''

	-- after every third character:
	DECLARE @i INT
	IF LEN(@before)>3 
	BEGIN
		SET @i = 3
		WHILE @i>1 and @i < len(@before)
		BEGIN
			SET @before = substring(@before,1,len(@before)-@i) + ',' + right(@before,@i)
			SET @i = @i + 4
		END
	END
	SET @return_value = @before + @after

	IF @is_negative = 1
		SET @return_value = '-' + @return_value

	RETURN @return_value 
END