LeetCode-SQL-569. 员工薪水中位数_编写sql查找每个公司的薪水中位数

sql架构

Create table If Not Exists Employee (Id int, Company varchar(255), Salary int)
Truncate table Employee
insert into Employee (Id, Company, Salary) values ('1', 'A', '2341')
insert into Employee (Id, Company, Salary) values ('2', 'A', '341')
insert into Employee (Id, Company, Salary) values ('3', 'A', '15')
insert into Employee (Id, Company, Salary) values ('4', 'A', '15314')
insert into Employee (Id, Company, Salary) values ('5', 'A', '451')
insert into Employee (Id, Company, Salary) values ('6', 'A', '513')
insert into Employee (Id, Company, Salary) values ('7', 'B', '15')
insert into Employee (Id, Company, Salary) values ('8', 'B', '13')
insert into Employee (Id, Company, Salary) values ('9', 'B', '1154')
insert into Employee (Id, Company, Salary) values ('10', 'B', '1345')
insert into Employee (Id, Company, Salary) values ('11', 'B', '1221')
insert into Employee (Id, Company, Salary) values ('12', 'B', '234')
insert into Employee (Id, Company, Salary) values ('13', 'C', '2345')
insert into Employee (Id, Company, Salary) values ('14', 'C', '2645')
insert into Employee (Id, Company, Salary) values ('15', 'C', '2645')
insert into Employee (Id, Company, Salary) values ('16', 'C', '2652')
insert into Employee (Id, Company, Salary) values ('17', 'C', '65')

SELECT
    Employee.Id, Employee.Company, Employee.Salary
FROM
    Employee,
    Employee alias
WHERE
    Employee.Company = alias.Company
GROUP BY Employee.Company , Employee.Salary
HAVING SUM(CASE
    WHEN Employee.Salary = alias.Salary THEN 1
    ELSE 0
END) >= ABS(SUM(SIGN(Employee.Salary - alias.Salary)))
ORDER BY Employee.Id
;

SELECT 
    Id, Company, Salary
FROM
    (SELECT 
        e.Id,
        e.Salary,
        e.Company,
        IF(@prev = e.Company, @Rank:=@Rank + 1, @Rank:=1) AS rank,
        @prev:=e.Company
    FROM
        Employee e, (SELECT @Rank:=0, @prev:=0) AS temp
    ORDER BY e.Company , e.Salary , e.Id) Ranking
        INNER JOIN
    (SELECT 
        COUNT(*) AS totalcount, Company AS name
    FROM
        Employee e2
    GROUP BY e2.Company) companycount ON companycount.name = Ranking.Company
WHERE
    Rank = FLOOR((totalcount + 1) / 2)
        OR Rank = FLOOR((totalcount + 2) / 2)
;