2019独角兽企业重金招聘Python工程师标准>>> 
第一步：创建表及数据：
create table uid(
uid int, --uid
cate varchar(20), --类别
price double --金额
)
insert into uid values(123,'c1',21);
insert into uid values(123,'c2',23);
insert into uid values(123,'c3',14);
insert into uid values(123,'c4',25);
insert into uid values(123,'c8',10);
insert into uid values(124,'c1',28);
insert into uid values(124,'c15',25);
insert into uid values(124,'c2',12);
insert into uid values(124,'c31',40);
insert into uid values(124,'c7',15);
查询结果：
第二步：取uid的金额最多的前四名
1.获取所有记录
2.增加序列并过滤（增加序列需要排序）：
4.完成并查询结果：
