Mysql查询应用

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1.分数排名

对Scores表(左二列)返回分数排名(右二列)，名词之间不可有间隔

select Score,dense_rank() over(order by Score desc) as "Rank" from Scores;

2.连续出现的数字

对Logs表(左二列)返回至少连续出现3次的数字(右一列)

select distinct Num as ConsecutiveNums
from(
    select num,
    @times:=if(@prenum=num,@times:=@times+1,1) as times,
    @prenum:=num
    from
    Logs,(
        select @prenum:=null,
        @times:=0
    ) as t
) as a
where a.times>2;

定义临时变量prenum表示前一数字，times表示连续出现次数
若前一数字来自于与本次数字相同则times加一，最后筛选times>2的结果；

3.超过经理收入的员工

对Employee表(左四列)返回员工工资大于其经理工资的员工姓名(右一列)

select a.Name Employee from Employee a join Employee b where a.MangerId=b.Id and a.Salary > b.Salary;

内连接，将Employee表中员工工资与其经理工资进行关联

4.查找重复的电子邮箱

对Person表(左二列)返回所有重复的电子邮箱(右一列)

select Email from Person group by Email having count(Email)>1;

5.从不订购的客户

对Customers表(左二列)和Orders表(中二列)返回从不订购任何东西的客户(右一列)

select Name Customers from Customers left join Orders on Customers.Id=Orders.CustomerId where Orders.Id is null;

6.部门工资最高/前三高的员工

对Employee表(左四列)和Department表(中二列)返回各部门工资最高的员工信息(右三列)

select S.Department,S.Employee,S.Salary from(
    select D.Name Department,E.Name Employee,E.Salary,
            dense_rank() over(partition by E.DepartmentId order by E.Salary desc) rk
    from Employee E inner join Department D on E.DepartmentId=D.Id
) as S where S.rk=1;

对Employee表(左四列)和Department表(中二列)返回各部门工资前三高的员工信息(右三列)

依旧使用以上程序，将条件语句改为S.rk<4即可

7.删除重复的电子邮箱

对Person表(左二列)删除重复邮箱并返回重复邮箱中Id最小的数据(右二列)

delete p1 from person p1,person p2 where p1.Email=p2.Email and p1.Id>p2.Id;

8.上升的温度

对Weather表(左三列)返回比上一天温度更高的Id(右一列)

select w1.Id from Weather w1 inner join Weather w2 on datediff(w1.RecordDate,w2.RecordDate)=1
where w1.Temperature>w2.Temperature;

9.大的国家

对World表(左五列)返回面积超过300万或人口超过2500万的国家(右三列)

select name,population,area from World where area>3000000
union
select name,population,area from World where population>25000000;

使用union取并集较优于or的多条件筛选（？）

10.受欢迎的课

对courses表(左二列)返回超过或等于5名学生的课(右一列)

select class from courses group by class having count(distinct student)>4;

Mysql查询应用

标签：ati   ble   大于   null   不可   mat   pop   count   应用   

原文地址：https://www.cnblogs.com/feifei-run/p/13406204.html