-- 013: system_no generation as a column DEFAULT (sequence-backed, 14 digits:
-- '20' + YY + 10-digit sequence). Unique index (012) remains the guarantee.

-- +up
CREATE SEQUENCE member_system_no_seq START 1;
ALTER TABLE members ALTER COLUMN system_no
  SET DEFAULT ('20' || to_char(now(), 'YY') || LPAD(nextval('member_system_no_seq')::text, 10, '0'));

-- +down
ALTER TABLE members ALTER COLUMN system_no DROP DEFAULT;
DROP SEQUENCE IF EXISTS member_system_no_seq;