Listing 5: Function That Converts Value from Original Base to Decimal
CREATE FUNCTION dbo.fn_basetodec
   (@val AS VARCHAR(63), @base AS int)
  RETURNS BIGINT
AS
BEGIN
  RETURN
    (SELECT SUM(
       (CHARINDEX(
          SUBSTRING(@val, LEN(@val) - n + 1, 1),
          '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ') - 1)
       * POWER(CAST(@base AS BIGINT), n-1))
     FROM Nums
     WHERE n <= LEN(@val));
END
GO