CREATE VIEW 按性别汇总(性别，人数)
AS
SELECT `性别`,COUNT(*)
FROM student
GROUP BY `性别`

SELECT `性别`,人数
FROM(SELECT `性别`,COUNT(*) AS 人数FROM studentGROUP BY `性别`
)AS 按性别汇总

SELECT `学号`,`成绩`
FROM score
where `成绩` in(SELECT MIN(`成绩`)FROM scoreGROUP BY `课程号`
)

SELECT `学号`,`成绩`
FROM score
where `成绩` >ANY(SELECT `成绩`FROM scoreWHERE `课程号`='0002'
)

SELECT `学号`,`成绩`
FROM score
where `成绩` >(SELECT AVG(`成绩`)  --返回一个81.125单一的值FROM score
)

SELECT `学号`,`成绩`,(SELECT AVG(`成绩`)FROM score
)AS 平均成绩
FROM score

SELECT `学号`,`课程号`,成绩
FROM score AS s1
WHERE 成绩 > (SELECT AVG(`成绩`)FROM score s2WHERE s1.`课程号`= s2.`课程号` --关联条件，可以在每个组里比较GROUP BY `课程号`
)

SELECT name FROM worldWHERE population >(SELECT population FROM worldWHERE name='Russia')select name from world
where continent= 'Europe' and gdp/population >
(select gdp/population from worldwhere name ='United Kingdom') SELECT name,continent FROM worldWHERE continent In(SELECT continent FROM worldWHERE name='Argentina' or name='Australia')
order by name4.查找符合下面条件的国家名称和人口：国家的人口比加拿大(Canada)的多，但比波兰(Poland)的少在运算符between里使用标量子查询，这里用between查找出的范围边界值包括了边界值比如范围是 1=<x<=10，为了不包括边界值，需要去掉两个边界值，变成 1+1=<x<= (10-1)
select name, population
from world
where population between
(select population
from world
where name='Canada')+1 and
(select population
from world
where name='Poland')-1;select name, concat(round(population /(select population from world where name='Germany')*100,0),'%')
from world
where continent = 'Europe';select name
from world
where gdp > all
(select gdp from world
where continent = 'Europe' and gdp > 0);select continent,name,area
from world as x
where area =
(select max(area)
from world as y
where y.continent=x.continent);select continent, name
from world as x
where name <= all
(select name
from world as y
where y.continent=x.continent);select name, continent, population
from world as x
where 25000000 >= all
(select population
from world as y
where y.continent=x.continent);select name, continent
from world as x
where population > all
(select 3*population
from world as y
where y.continent=x.continent and x.name <> y.name
);