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`
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`