Problems

https://leetcode.com/problemset/database/

175. Combine Two Tables

# Write your MySQL query statement below
select FirstName,LastName,City,State
from Person left join Address 
on Person.PersonId = Address.PersonId;

176. Second Highest Salary

# Write your MySQL query statement below
select max(Salary) as SecondHighestSalary
from Employee 
where Salary < (select max(Salary) from Employee);

177. Nth Highest Salary

select * from tablename limit 0,1

即取出第一条记录。

select * from tablename limit 1,1

第二条记录

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

178. Rank Scores

# Write your MySQL query statement below
select Score,(select count(1)+1
                from (select distinct Score ss
                        from Scores
                     ) tmp
                where ss > Score
              ) Rank
from Scores
order by Score desc

180. Consecutive Numbers

# Write your MySQL query statement below
select distinct l1.Num as ConsecutiveNums
from Logs l1,Logs l2,Logs l3
where l1.Id = l2.Id - 1 and l1.Id = l3.Id - 2 and l1.Num = l2.Num and l2.Num = l3.Num;

181. Employees Earning More Than Their Managers

# Write your MySQL query statement below
select a.Name as Employee
from Employee a,Employee b
where a.ManagerId = b.Id and a.Salary > b.Salary;

182. Duplicate Emails

# Write your MySQL query statement below
select Email
from Person
group by Email
having count(1) > 1;

183. Customers Who Never Order

# Write your MySQL query statement below
select Name as Customers
from Customers
where Id not in
(
    select distinct CustomerId
    from Orders
);

184. Department Highest Salary

# Write your MySQL query statement below
select Department.Name Department,Employee.name Employee,Salary
from 
(
    select Department.Name,Max(Salary) maxs
    from Department,Employee
    where Employee.DepartmentId = Department.Id
    group by Department.Name
) tmp,Department,Employee
where tmp.Name = Department.Name and Employee.DepartmentId = Department.Id and Salary = maxs;

185. Department Top Three Salaries

# Write your MySQL query statement below
select d.Name Department,e.name Employee,Salary
from Employee e,Department d
where DepartmentId = d.Id and (select count(distinct(e2.Salary))
                             from Employee e2
                             where e.DepartmentId = e2.DepartmentId and e.Salary < e2.Salary) < 3
order by d.Id,Salary desc;

196. Delete Duplicate Emails

# Write your MySQL query statement below
delete a
from Person a,Person b
where a.Email = b.Email and a.Id > b.Id;

197. Rising Temperature

# Write your MySQL query statement below
select a.Id
from Weather a,Weather b
where TO_DAYS(a.Date)=TO_DAYS(b.Date)+1 and a.Temperature > b.Temperature;

262. Trips and Users

# Write your MySQL query statement below
select Request_at Day,round(sum(case when Status = 'completed' then 0 else 1 end) / count(1) ,2) 'Cancellation Rate'
from Trips 
where Client_Id in
(
    select Users_Id
    from Users
    where Banned = 'No' and Role = 'client'
) and Request_at >= '2013-10-01' and Request_at <= '2013-10-03'
group by Request_at;