题解 | 统计作答次数
统计作答次数
https://www.nowcoder.com/practice/45a87639110841b6950ef6a12d20175f
if()条件判断函数：
根据条件返回不同结果，用于数据统计等场景
语法：
if(条件表达式，条件为真时返回值，条件为假时返回值)
代码如下：
select
count(exam_id) as total_pv,
count(submit_time) as complete_pv,
count(distinct if(submit_time is not null, exam_id, null)) as complete_exam_cnt
from exam_record;
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