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题解 | #平均活跃天数和月活人数#

select date_format(submit_time,'%Y%m') as month,round(count(distinct uid,date_format(submit_time,'%Y%m%d'))/count(distinct uid),2) avg_active_days,rou...

Mysql

2022-02-22

0 303

题解 | #得分不小于平均分的最低分#

#提交时返回了一个none值，后来发现是不小于忘记取等了，导致等于的这种情况就没有值，变成了none select min(score) min_score_over_avg from exam_record er join examination_info ei on er.exam_id = e...

Mysql

2022-02-21

0 294

题解 | #统计作答次数#

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

Mysql

2022-02-21

0 286

题解 | #SQL类别高难度试卷得分的截断平均值#

select ei.tag,ei.difficulty,round((sum(score)-max(score)-min(score))/(count(score)-2),1) clip_avg_score from examination_info ei join exam_record er o...

Mysql

2022-02-21

0 300

题解 | #删除索引#

drop index uniq_idx_exam_id on examination_info; drop index full_idx_tag on examination_info; alter table examination_info drop index full_idx_tag;

Mysql

2022-02-21

0 289

题解 | #创建索引#

create index idx_duration on examination_info(duration); create unique index uniq_idx_exam_id on examination_info(exam_id); create fulltext index full...

Mysql

2022-02-21

0 263

题解 | #修改表#

alter table user_info add school varchar(15) after level; alter table user_info change job profession varchar(10); alter table user_info modify achiev...

Mysql

2022-02-21

0 303

题解 | #创建一张新表#

create table if not exists user_info_vip( id int(11) primary key auto_increment comment "自增ID", uid int(11) unique not null Comment "用户ID", nick_name ...

Mysql

2022-02-21

0 352

题解 | #删除记录（二）#

delete from exam_record where submit_time is null or timestampdiff(minute,start_time,submit_time) < 5 order by start_time asc limit 3; #limit 0,3报错...

Mysql

2022-02-21

0 230

题解 | #插入记录（三）#

delete from examination_info where exam_id = 9003; insert into examination_info values(null,9003,"SQL","hard",90,"2021-01-01 00:00:00");

Mysql

2022-02-21

0 332