题解 | #SQL15 统计作答次数#

方法一：子查询

select count(start_time) total_pv,
count(submit_time) complete_pv,
(
    select count(distinct(exam_id)) from exam_record where submit_time is not null
) complete_exam_cnt
from exam_record;

方法二：

select count(start_time) total_pv,
count(submit_time) complete_pv,
count(distinct(exam_id) and submit_time is not null)
from exam_record;