题解 | #统计复旦用户8月练题情况#

SELECT up.device_id,'复旦大学' as university,
count(question_id) as question_cnt,
sum(if(qpb.result='right',1,0)) as right_question_cnt
from user_profile up
left join
question_practice_detail as qpb
on up.device_id=qpb.device_id and month(date)=8
where up.university='复旦大学'
group by up.device_id 

需求分析：查找university=复旦，month(date)=8 的 count(question_id) 做题数量,sum(if(result='right',1,0)) 正确的题目量

解决思路:连表查询，注意if（）使用方式