More protection

One more thing: numbers only Still okay to check elsewhere: levels of logic

CREATE OR REPLACE FUNCTION validate_ccnumber(VARCHAR)
RETURNS BOOLEAN AS '
DECLARE
  mynumber ALIAS FOR $1;
BEGIN

  -- Must be 16 characters long
  IF length(mynumber) != 16 THEN
    RAISE EXCEPTION \'Credit card numbers must be 16 digits long\';
  END IF;

  -- Must be number 0-9 only
  IF length(substring(mynumber FROM \'[^\\\\d]\')) THEN
    RAISE EXCEPTION \'Credit card number must have only digits 0-9\';
  END IF;

  -- Must have a valid checksum
  IF cc_checksum(mynumber) THEN
    RAISE EXCEPTION \'Invalid credit card number: checksum failed\n';
  END IF;

  RETURN TRUE;
END;
' LANGUAGE plpgsql IMMUTABLE;

oscon=> insert into biz values ('123412341234123a');
ERROR:  Credit card number must have only digits 0-9

Can we do better?