题目:左连接Person表和Address表。
select FirstName,LastName,City,State from Person p left join Address a on p.PersonId=a.PersonId;
7个case耗时1001ms(注意耗时多次提交会不同,一般相差不大,偶尔也有相差大的) --2015/1/11
题目:写一条sql语句查询Employee
表中第二高工资值。
select max(Salary ) from Employee where Salary not in(select max(Salary ) from Employee)
7个case耗时1001ms --2015/1/11
查询第n大的值。
CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT BEGIN DECLARE M INT; SET M=N-1; RETURN ( # Write your MySQL query statement below. SELECT IFNULL((SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT M ,1), NULL) ); END #14 cases 925ms
178 Rank Scores
按得分排名并计算排名。
select Scores.score,count(Ranking.Score) as rank from Scores, (select distinct score from Scores) Ranking where Scores.score <= Ranking.Score group by Scores.id,Scores.score order by Scores.score desc; #955ms
找出至少连续出现3次的Num。这道题确实不知道怎么下手,看了答案理解了一下。
select DISTINCT num FROM (select num, case when @record = num then @count:=@count+1 when @record <> num then @count:=1 end as n from Logs ,(select @count:=0,@record:=(SELECT num from Logs limit 0,1)) r ) a where a.n>=3
这个居然也可以过?
select distinct(a.Num) from Logs a, Logs b,Logs c where a.Id=b.Id+1 and a.Num=b.Num and b.Id=c.Id+1 and b.Num=c.Num #21 cases 1577ms
181 Employees Earning More Than Their Managers
查询工资比上司高的员工。
select a.name as Employee from Employee a left join Employee b on a.ManagerId = b.Id where a.Salary>b.Salary #14 cases 1336ms
select a.Name from Employee a inner join Employee b on a.ManagerId=b.Id where a.Salary>b.Salary #用内联时间应该更短
182 Duplicate Emails
题目:查找表中有重复的emails。
这里提供四种方法:
select Email from Person group by Email having count(*) > 1; #14 cases 1069ms select distinct a.Email from Person a join Person b on (a.Email = b.Email) where a.Id <> b.Id;#14 cases 1048ms select distinct a.Email from Person a where exists(select 1 from Person b where a.Email = b.Email limit 1, 1); #14 cases 1138ms select distinct a.Email from Person a left join (select Id,Email from Person group by Email) b on (a.Email = b.Email) and (a.Id=b.Id) where b.Email is NULL;#14 cases 1060ms
题目:查出没有订单的客户。
select Name as Customers from Customers where Id not in(select distinct(CustomerId) from Orders); #693ms
题目:查询每个部门最高的工资。
select D.Name as Department, E.Name as Employee, E.Salary as Salary from Employee E ,Department D where E.DepartmentId=D.Id AND (DepartmentId,Salary) in (SELECT DepartmentId,max(Salary) as max FROM Employee GROUP BY DepartmentId) ;#1736ms