176.第二高的薪水 select ( select DISTINCT Salary #去重 from Employee ORDER BY Salary DESC #降序排列 limit 1 offset 1 #從第一條資料讀取（offset 1 ，但不包括第一條），往後讀取一條資料（limit1 ），即第二條； ) as SecondHighestSalary;

596. 超過5名學生的課 SELECT class from courses group by class having count(DISTINCT student) >= 5;

197. 上升的溫度

select Id from Weather a, Weather b where a.Temperature > b.Temperature and DATEDIFF(a.RecordDate, b.RecordDate) = 1

196. 刪除重複的電子郵箱

DELETE p2 FROM Person as p1, Person as p2 wHERE p1.Email = p2.Email AND p2.Id > p1.Id

181. 超過經理收入的員工

SELECT Worker.Name AS Employee FROM Employee AS Worker, Employee AS Manager WHERE Worker.ManagerId = Manager.Id AND Worker.Salary > Manager.Salary 183. 從不訂購的客戶

select Name as Customers from Customers where Id not in( select C.Id from Customers as C, Orders as O where C.Id = O.CustomerId)

175. 組合兩個表

SELECT FirstName, LastName, City, State FROM Person LEFT JOIN Address ON Person.PersonId = Address.PersonId

595. 大的國家

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

182. 查詢重複的電子郵箱

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

627. 交換工資

UPDATE salary SET sex = (CASE WHEN sex = 'm' THEN 'f' ELSE 'm' END)

620. 有趣的電影

select * from cinema where description<>'boring' and MOD(id,2)=1 ORDER BY rating desc