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题解 | #统计每个学校各难度的用户平均刷题数#

select up.university, qd.difficult_level, count(qpd.question_id)/count(distinct up.device_id) #注意，问题数量可有重复，但设备（即用户）不能重复 from user_prof...

Mysql

2022-01-07

1 369

题解 | #浙江大学用户题目回答情况#

方法一连表查询 select qpd.device_id,qpd.question_id,qpd.result FROM question_practice_detail as qpd inner join user_profile as up on qpd.device_id = up.devi...

Mysql

2021-12-31

0 417

题解 | #浙江大学用户题目回答情况#

# 方法一连表查询 # select qpd.device_id,qpd.question_id,qpd.result FROM # question_practice_detail as qpd inner join user_profile as up on qpd.device_id = u...

Mysql

2021-12-31

2 388

题解 | #获取有奖金的员工相关信息。#

select e.emp_no , e.first_name , e.last...

Mysql

2021-09-30

0 388

题解 | 三表连接

旧SQL语句: SELECT DISTINCT ( m.music_name ) FROM follow AS f LEFT JOIN music_likes AS ml ON f.follower_id = ml.user_id INNER JOIN music AS m ON ml.m...

Mysql

2021-09-30

10 1645

题解 | #获得积分最多的人(一)#

# 方法一 select gs.name , max(`grade_sum`) from ( SELECT u.name , SUM(g.grade_num) as `grade_sum` FROM user as u inner join grade_info as g on u.id...

Mysql

2021-09-23

3 595

题解 | #统计各个部门的工资记录数#

解题思路：首先把部门表departments、部门员工关系表dept_emp、薪水表salaries三表连接，得到下图所示的新表，然后根据题目要求和以下新表就能写出对应的sql语句（注：使用inner join连接时，一般为： (行数多的表) inner join (行数少的表) on ...

2021-08-24

1 520

题解 | #获取所有员工当前的manager#

错误方法示范： SELECT emp_no , max(salary)-min(salary) as growth from salaries where emp_no in ( SELECT emp_no from salaries where to_date = "9999-01-...

2021-08-23

5 493

题解 | #找出所有员工当前薪水salary情况#

#方法1：in/ not in # select emp_no # from employees as e # where emp_no not IN # ( # select e.emp_no from employee...

2021-08-19

3 531

题解 | #查找当前薪水详情以及部门编号dept_no#

SELECT dm.emp_no ,s.salary ,s.from_date, dm.to_date ,dm.dept_nofrom salaries as s inner join dept_manager as dmon s.emp_no = dm.emp_no

2021-08-19

1 477