mysql group by/having/distinct 查询使用例子

表的内容如下：

//查询单分数最高的人ID

select stuid,max(score) from stu_select_class;

// 查询各科总分2-3名的学生
select stuid, sum(score) from stu_select_class group by stuid  limit 1,2;

//查询每科的最高分学生
select classname,stuid,max(score) from stu_select_class group by classname;

//查询总分低于140的学生
select stuid, sum(score) from stu_select_class group by stuid having sum(score)<140;

//查询总平均分在60-80的学生
select stuid, avg(score) from stu_select_class group by stuid having avg(score) between 60 and 80;

//查询。。。。的学生
select stuid, sum(score),avg(score) from stu_select_class group by stuid having sum(score)<140 and avg(score) <80;
//查询总分。。的学生人数。
select distinct count( stuid)  from stu_select_class group by stuid having sum(score)<140 and avg(score) <80;
//查询。。。的学生人数
select count(distinct stuid) from stu_select_class where classname='english' and score <100;