select * from user where city='北京'order by credit;
select * from user where sex='男' order by personId desc;
select * from user where ename is not null order by ename ;
select city,count(userId) from user group by city;
select sex,avg(credit) from user group by sex;
select * from user where credit order by credit desc limit 0,3
select * from user where sex='男' order by credit limit 0,3
select city,avg(credit) from user group by city having avg(credit)>350;