题解 | #统计作答次数#
统计作答次数
http://www.nowcoder.com/practice/45a87639110841b6950ef6a12d20175f
select
COUNT(exam_id) as total_pv,
count(submit_time) as complete_pv,
# 先去重exam_id 并且分数 不为空
count(distinct exam_id and score is not null) as complete_exam_cnt
from exam_record e
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