题解 | #统计复旦用户8月练题情况#
统计复旦用户8月练题情况
http://www.nowcoder.com/practice/53235096538a456b9220fce120c062b3
1.left join 左边的表全部保留，可以留下八月份没有做题的学生
2.sum(if(result = 'right',1,0)) 答题正确，进行累加计数
3.group by u.device_id 根据学生id分组
select u.device_id, university, count(question_id) as question_cnt, sum(if(result='right',1,0)) as right_question_cnt from user_profile u left join question_practice_detail q on u.device_id = q.device_id and date like '%-08-%' where university = '复旦大学' group by u.device_id
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