ALTER TABLE pro_sit_trib
  ADD COLUMN calcula_difal character varying(1);

UPDATE pro_sit_trib SET calcula_difal = 'S' WHERE SUBSTR(LPAD(codigo::TEXT, 3, '0'), 2, 2) IN('00', '10', '20', '70', '90') AND calcula_difal IS NULL;
UPDATE pro_sit_trib SET calcula_difal = 'N' WHERE calcula_difal IS NULL;


ALTER TABLE pro_sit_trib
  ALTER COLUMN calcula_difal SET NOT NULL;