SELECT up.device_id,'复旦大学',COUNT(qpd.question_id),SUM(CASE WHEN qpd.result='right' THEN 1 ELSE 0 END) FROM user_profile up LEFT JOIN question_practice_detail qpd ON up.device_id=qpd.device_id
WHERE university='复旦大学'AND( MONTH(qpd.date)='8' OR qpd.date iS NULL) GROUP BY up.device_id; #sum(if(qpd.result='right', 1, 0))这个if条件函数的使用是真的很骚。。然后就是if条件函数外加sum函数