Order-Preserving Base-58

opb58enc-mssql.sql

-- num <= 430804206899405823: <= 10 digits
-- num > 430804206899405823: 11 digits
CREATE FUNCTION opb58enc (@num bigint) RETURNS char(11) WITH SCHEMABINDING AS
BEGIN
  DECLARE @alphabet char(58) = '0123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz'
  DECLARE @encoded varchar(11)
  DECLARE @divisor bigint
  DECLARE @mode int = 0

  SET @encoded = ''

  WHILE @num  >= 58 BEGIN
    SET @divisor = @num / 58
    SET @mode = @num - 58 * @divisor
    SET @encoded = CONCAT(SUBSTRING(@alphabet, @mode + 1, 1), @encoded)
    SET @num = @divisor
  END

  RETURN CONCAT(SUBSTRING(@alphabet, @num + 1, 1), @encoded)
END