SELECT u.`id`,u.`user_id`,u.`name` FROM USER u LEFT JOIN user_dept ud ON u.`id`=ud.`user_id` LEFT JOIN dept d ON ud.`dept_id`=d.`id` WHERE d.`id`=1 GROUP BY u.`id`
三表联查
原文：http://www.cnblogs.com/lusufei/p/7587358.html
