ALTER TABLE waterway.waterway_axis
    ADD validity tstzrange NOT NULL DEFAULT tstzrange(current_timestamp, NULL)
        CHECK (NOT isempty(validity)),
    ADD last_found timestamp with time zone NOT NULL DEFAULT current_timestamp;

-- Assume existing entries have been valid since last import
UPDATE waterway.waterway_axis SET validity = tstzrange(
    (SELECT max(changed) FROM import.imports WHERE kind = 'wx'),
    NULL);

DROP TRIGGER waterway_axis_wtwaxs_unique ON waterway.waterway_axis;
CREATE CONSTRAINT TRIGGER waterway_axis_wtwaxs_unique
    AFTER INSERT OR UPDATE OF wtwaxs, validity ON waterway.waterway_axis
    FOR EACH ROW EXECUTE FUNCTION prevent_st_equals('wtwaxs', 'validity');

CREATE INDEX waterway_axis_validity
    ON waterway.waterway_axis USING GiST (validity);

-- No more need to delete
DROP POLICY responsibility_area_delete ON waterway.waterway_axis;