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题解 | #提取博客URL中的用户名#

select device_id, substring_index(blog_url, '/', -1) as user_name from user_submit 和上一题一样用到 su...

Mysql

2022-05-24

0 281

题解 | #截取出年龄#

```select substring_index(substring_index(profile, ',', -2), ',', 1) as age, count(device_id) as number from user_submit group by age substr...

Mysql

2022-05-24

0 329

题解 | #统计每种性别的人数#

第一种比较笨笨 ```select 'female' as gender, count(*) as number from user_submit where profile like '%female' union all select 'm...

Mysql

2022-05-24

0 291

题解 | #计算用户8月每天的练题数量#

```select day(date) as day, count(question_id) as question_cnt from question_practice_detail where month(date) = 08 and year(date) = 2021 group by dat...

Mysql

2022-05-24

0 250

题解 | #计算25岁以上和以下的用户数量#

```select '25岁以下' as age_cut, count(device_id) as number from user_profile where age < 25 or age is null union select '25岁及以上' as age_cut, count(de...

Mysql

2022-05-24

0 296

题解 | #查找山东大学或者性别为男生的信息#

学会了 union all是可以不去重的！！感谢大佬 select device_id, gender, age, gpa from user_profile where university='山东大学' union all select device_id, gende...

Mysql

2022-05-24

0 299

题解 | #统计每个学校各难度的用户平均刷题数#

select u.university, qd.difficult_level, count(qpd.question_id) / count(distinct qpd.device_id) as avg_answer_cnt from question_practice_detail qpd jo...

Mysql

2022-05-23

0 570

题解 | #统计每个学校的答过题的用户的平均答题数#

select u.university, count(question_id) / count(distinct u.device_id) as avg_answer_cnt from user_profile u right join question_practice_detail q on u...

Mysql

2022-05-23

0 290