CREATE FUNCTION reorder_priority() RETURNS TRIGGER AS $$
BEGIN
    CASE TG_OP
        WHEN 'UPDATE' THEN
            UPDATE
                link
            SET
                priority = priority + 1
            WHERE
                link.priority >= NEW.priority AND
                NOT link.priority > OLD.priority;
    END CASE;
    RETURN NULL;
END;
$$ LANGUAGE plpgsql;正确解法
BEGIN
    CASE TG_OP
        WHEN 'UPDATE' THEN
            UPDATE
                link
            SET
                priority = priority + 1
            WHERE
                link.priority >= NEW.priority AND
                NOT link.priority >= OLD.priority;
    END CASE;
    RETURN NEW;
END;