LeetCode Problems

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1. Database

   Easy

    627. Swap Salary
    update salary set sex = if(sex = 'm', 'f', 'm')
    
    596. Classes More Than 5 Students
    select c.class from courses c group by c.class having count(distinct c.student) > 4
    #tips：一个学生同选一门课无效(distinct)
   
    595. Big Countries
    select name, population, area from World where(area > 3000000 or population > 25000000)
   
    620. Not Boring Movies
    select * from cinema where(description != 'boring' and id%2 = 1) order by rating desc
   
    197. Rising Temperature
    SELECT w1.Id FROM Weather w1, Weather w2 WHERE w1.Temperature > w2.Temperature AND DATEDIFF(w1.RecordDate, w2.RecordDate) = 1;
   
    196. Delete Duplicate Emails
    delete p1 from Person p1, Person p2 where p1.Email=p2.Email and p1.Id>p2.Id
   
    183. Customers Who Never Order
    SELECT Name as Customers FROM Customers c WHERE c.Id NOT IN (SELECT CustomerId FROM Orders o)
   
    182. Duplicate Emails
    select Email from Person group by email having count(Email) > 1
   
    181. Employees Earning More Than Their Managers
    select e.Name as Employee from employee e,employee m where e.managerid=m.id and e.salary>m.salary
    #将表作为两个镜像别名表来对比
   
    176. Second Highest Salary
    select ifnull((select Distinct Salary from Employee order by Salary desc limit 1,1), null) as SecondHighestSalary
   
    175. Combine Two Tables
    select p.FirstName, p.LastName, a.City, a.State from Person p left join Address a on p.PersonId = a.PersonId
   

2. Algorithms

3. Shell