[大数据]数据库函数

– 求学生表的学生总人数
select count(*) from tb_stu

– 求学生表的学生年龄总和
select sum(age) from tb_stu

– 查找学生表里年龄最大的数
select min(age) from tb_stu

– 求学生表平均年龄
select avg(age) from tb_stu

– 求学生表里男女生分别的平均年龄
select sex,avg(age) from tb_stu group by sex

– 求学生表男女生姓张的总人数分别是多少
select sex,count(*) from tb_stu where sname like ‘张%’ group by sex

– 求学生表里各个国家地址分别的总和
select address,count(*) from tb_stu group by address

– 查找学生表里地址人数超过1个人的地方
select address from tb_stu group by address having count(*)>1

– where是在过滤后进行分组，having是在分组后过滤
– 查找学生表里男生人数大于1的地方
select address from tb_stu where sex='男’group by address having count(*)>1

数字函数、日期函数：

https://www.runoob.com/mysql/mysql-functions.html