3、SQL基础整理（分组）

分组

group by

select class from xuesheng group by class

 

select class,AVG(chinese)from xuesheng group by class

 

select math from xuesheng where math >80 group by math

 

select math from xuesheng where math between 80 and 90 group by math

 

select math,count(*) from xuesheng where math between 80 and 90 group by math

 

选出语文成绩>80的班级行总数，按班级分组

select class,COUNT(*)from xuesheng where chinese>80 group by class

 

having 后面只能加聚合函数（从表中选出where后，先看前面的聚合函数，再算后面的聚合函数）

select class,COUNT(*)from xuesheng where chinese>=80 group by class having COUNT(*)>10

 

select class,COUNT(*),AVG(math)from xuesheng group by class having AVG(math)>90

 

select class,COUNT(*) from xuesheng where math>80 group by class order by COUNT(*)

 

--分别求每个班语数外最高分，并按语文升序排序

select class,MAX(chinese),MAX(math),MAX(english) from xuesheng group by class order by MAX(chinese)