比较复杂的sql面试题

一、分组统计每个班的分数前三名（等同于LeetCode：185. Department Top Three Salaries）

表结构：

create table student(

id varchar(20),-- 编号

class varchar(20),-- 年级

score int-- 分数

);

insert student values('1','一年级',82);

insert student values('2','一年级',95);

insert student values('3','一年级',82);

insert student values('4','一年级',40);

insert student values('5','一年级',20);

insert student values('6','二年级',95);

insert student values('7','二年级',40);

insert student values('8','二年级',3);

insert student values('9','二年级',60);

insert student values('10','二年级',10);

insert student values('11','三年级',70);

insert student values('12','三年级',60);

insert student values('13','三年级',40);

insert student values('14','三年级',90);

sql：

select a.class,a.score 
from student a 
where (select count(*) from student where class=a.class and a.score<score)<3
order by a.class,a.score desc;

二、LeetCode：262. Trips and Users

题目详见：https://leetcode.com/problems/trips-and-users/

sql：

SELECT Request_at Day,
       ROUND(SUM(IF(Status = 'completed', 0, 1)) / COUNT(*), 2) 'Cancellation Rate'
FROM   Trips t
LEFT   JOIN Users t1 ON t.Client_Id = t1.Users_Id
WHERE  t1.Banned = 'No' AND Request_at BETWEEN '2013-10-01' AND '2013-10-03'
GROUP  BY t.Request_at;