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题解 | #得分不小于平均分的最低分#

with t as ( # 这里 over() 是开窗函数，表示将平均值放到一整列上 # 具体参考这个博客：[链接](https://blog.csdn.net/qq_22508585/article/details/79334811?ops_request_misc=%257B%2...

Mysql

2021-12-09

0 440

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...

Mysql

2021-12-08

0 384

题解 | #SQL14 SQL类别高难度试卷得分的截断平均值#

# 先查一个小表 with t as (SELECT ei.tag, ei.difficulty, er.score FROM examination_info ei, exam_record er where ei.tag = 'SQL' and ei.difficulty = 'hard' an...

Mysql

2021-12-08

0 474

题解 | #SQL39 21年8月份练题总数#

select count(distinct(device_id)) did_cnt, count(question_id) question_cnt from question_practice_detail where Month(date) = '08';

Mysql

2021-12-06

0 353

题解 | #SQL35 浙大不同难度题目的正确率#

SELECT qd.difficult_level, # 这里分子用 sum，求该列上所有值的和；分母用 count，求有多少个非空行 sum(if(qpd.result = 'right', 1, 0)) / count(qpd.question_id) correct_rate # AVG(...

Mysql

2021-12-06

0 470

题解 | #SQL34 统计复旦用户8月练题情况#

首先根据以下代码获得初步结果： select * from user_profile u left JOIN question_practice_detail q # left join on 后面最好只放两者关联条件，不要放单独条件， # 例如 “u.university = '复旦大学'”，...

Mysql

2021-12-02

23 903

题解 | #SQL23 统计每个学校各难度的用户平均刷题数#

首先用以下代码获得多表查询的结果： select * from user_profile u, question_practice_detail qpd, question_detail qd where u.device_id = qpd.device_id and qpd.question_id...

Mysql

2021-11-30

0 450