题解 | 统计作答次数
统计作答次数
https://www.nowcoder.com/practice/45a87639110841b6950ef6a12d20175f
with t1 as(
select
exam_id,
count(start_time) a,
count(submit_time) b
from exam_record
group by exam_id
)
select
sum(a),
sum(b),
sum(if(b!=0,1,0))
from t1
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