LeetCode SQL - 码农教程

175.【简单】组合两个表

select p.FirstName,p.LastName,a.City,a.State from person p left join address a on p.personid=a.personid;

176.【简单】第二高的薪水

select ifnull((select distinct(Salary) from Employee order by Salary desc limit 1,1),null) as SecondHighestSalary;

177.【中等】第N高的薪水

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
set n=n-1;
  RETURN (
      # Write your MySQL query statement below.
      select distinct Salary as getNthHighestSalary
      from Employee
      order by Salary DESC
      limit N,1
  );
END

181.【简单】超过经理收入的员工

select e1.Name as Employee from Employee as e1,Employee as e2
where e1.Salary > e2.Salary and e1.ManagerId = e2.Id;

182.【简单】查找重复的电子邮箱

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

183.【简单】从不订购的客户

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

196.【简单】删除重复的电子邮箱

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

197.【简单】上升的温度

select w1.Id from Weather w1,Weather w2
where DATEDIFF(w1.RecordDate,w2.RecordDate)=1
and w2.Temperature<w1.Temperature;

595.【简单】大的国家

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

596.【简单】超过5名学生的课

select class from courses
group by class
having count(distinct student)>=5;

620.【简单】有趣的电影

select * from cinema
where description <> "boring" and id%2=1
order by rating desc;

627.【简单】交换工资

update salary set sex = if(sex="m" ,"f", "m")

1179.【简单】重新格式化部门表

SELECT DISTINCT id AS "id",
SUM(IF (month = "Jan", revenue, null)) AS "Jan_Revenue",
SUM(IF (month = "Feb", revenue, null)) AS "Feb_Revenue",
SUM(IF (month = "Mar", revenue, null)) AS "Mar_Revenue",
SUM(IF (month = "Apr", revenue, null)) AS "Apr_Revenue",
SUM(IF (month = "May", revenue, null)) AS "May_Revenue",
SUM(IF (month = "Jun", revenue, null)) AS "Jun_Revenue",
SUM(IF (month = "Jul", revenue, null)) AS "Jul_Revenue",
SUM(IF (month = "Aug", revenue, null)) AS "Aug_Revenue",
SUM(IF (month = "Sep", revenue, null)) AS "Sep_Revenue",
SUM(IF (month = "Oct", revenue, null)) AS "Oct_Revenue",
SUM(IF (month = "Nov", revenue, null)) AS "Nov_Revenue",
SUM(IF (month = "Dec", revenue, null)) AS "Dec_Revenue" 
FROM Department GROUP BY id