Function to determine credit card type from card number (SQL)

GetCardType.sql

-- create the function in SQL

CREATE FUNCTION [dbo].[GetCardType] (@CardNum varchar(100))
RETURNS varchar(10)
AS
BEGIN
	DECLARE @type varchar(10) 
	
	if (left(@CardNum, 1) = '4')
		begin
			set @type = 'VISA'
		end 
	else if (left(@CardNum, 2) = '34')
		begin
			set @type = 'AMEX'
		end
	else if (left(@CardNum, 2) = '37')
		begin
			set @type = 'AMEX'
		end
	else if (left(@CardNum, 2) = '65')
		begin
			set @type = 'DISC'
		end
	else if (left(@CardNum, 4) = '6011')
		begin
			set @type = 'DISC'
		end
	else
		begin
			set @type = 'MC'
		end

	RETURN @type
END
						      
						      
-- use the function in a query
						      
Select t.CardNumber, t.ExpirationDate, dbo.GetCardType(t.CardNumber) as CardType 	
From CardTable t