-- 1
select *
from user
where city='北京'
ORDER BY credit
-- 2
select *
from user
where sex='男' ORDER BY personId desc
-- 3
select *
from user
where ename is not null ORDER BY ename
-- 4
select city,count(name)
from user
GROUP BY city
-- 5
select sex , avg(credit)
from user
GROUP BY sex
-- 6
select *
from user
ORDER BY credit desc LIMIT 3
-- 7
select *
from user
where sex='男' ORDER BY credit LIMIT 3
-- 8
select city
from user
GROUP BY city
HAVING avg(credit)>350