b42

SELECT  c.user_id, SUM(c.amount)FROM (        SELECT d.user_id AS user_id, -(d.amount) AS amount        FROM demand d        WHERE d.cancel_date IS NULL        UNION ALL                SELECT p.user_id AS user_id, p.amount AS amount                FROM payment p                WHERE p.cancel_date IS NULL) cGROUP BY c.user_id