sql学习整理

1、group by 和 having 函数的应用

select max(msg_timestamp) as '最大秒数',count(distinct user_id) as '企微购房通用户数' from
 bb_wework_group_user_info where updated_at like '2022-01-19%'
group by msg_timestamp having max(msg_timestamp) ;

#例子：
#1、查找每个班中及格的学生的人数 
select class,count(*) from students group by class having grade>=60；
2、查找每个班中总成绩最优秀的学生 
select stu.class,max(stu.grade) from
(select stu,class,math_grade+chinese_grade as grade from students group by students）stu 
group by stu.class having max (stu.grade)；

2、distinct函数用途：去除表或列中的重复项。

#查出不重复的老师的数据
select distinct teacher_id from students ;