Validating Canadian Postal Codes

if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[CheckPostalCodeFormat]') and xtype in (N'FN', N'IF', N'TF'))
drop function [dbo].[CheckPostalCodeFormat]

GO
CREATE FUNCTION dbo.CheckPostalCodeFormat (@PostalCode nvarchar(10))
/******************************************************************************
**      Name: CheckPostalCodeFormat
**      Desc: Check the formatting of a postal code matches Canadian standards.
**              
**      Output Parameters:
**          @Result:  0 for no errors
**                   -1 for an error
**
**      Note:
**          input value is automatically uppercased with spaces removed, 
**          more stringent checking could be applied.
**
**      Auth: Ryan Brochez
**      Date: Nov-20-2006
*******************************************************************************/RETURNS bit
AS
BEGIN

    DECLARE @Result bit
    DECLARE @i int

    SET @Result = 0
    SET @i = 1
    SET @PostalCode = Upper(Replace(LTrim(@PostalCode), ' ', ''))

    -- Check the length
    IF Len(@PostalCode) <> 6 SET @Result = -1

    -- Character is alphanumerical (in the right position)
    ELSE 
        WHILE (@i <= 6) 
        BEGIN
            -- first character is alphabetical
            IF (@i%2 = 1) AND SubString(@PostalCode, @i, 1) NOT BETWEEN 'A' AND 'Z' 
                SET @Result = -1
            -- second character is numerical
            ELSE IF (@i%2 = 0) AND SubString(@PostalCode, @i, 1) NOT BETWEEN '0' AND '9' 
                SET @Result = -1    
            SET @i = @i + 1
        END

    RETURN @Result

END
GO

/*
-- test

-- return 0 for success 
select dbo.CheckPostalCodeFormat('A1B2C3')
select dbo.CheckPostalCodeFormat('d4E 5f6')

-- return -1 for failure
select dbo.CheckPostalCodeFormat('90210')
select dbo.CheckPostalCodeFormat('A11A1A1')

*/