·连接查询 ·group by 首先将三张表连接后查询,同时直接限定仅选择'浙江大学' SELECT up.device_id,university,qpd.question_id,qd.difficult_level as difficult_level,qpd.result as result from user_profile as up left join question_practice_detail as qpd on qpd.device_id=up.device_id left join question_detail as qd on qd.question_id=qpd...