day5 练习

employee表

id | name | sex | age | hire_date | post | salary |

添加的数据

部门名post 字段 teacher student sale it

hire_date 范围 2000-01-01 -------2019-12-12

插入6条数据进行以下筛选 

1.每个部门的人数

select post, count(id) from employee group by post; 

2.每个部门男性的数量

结果select count(id)

条件 where sex="male" group by post

select post,count(id) from employee where sex="male" group by post;

3.每个部门平均工资小于10000的员工数量 

结果 select count(id)

条件 group by post having avg(salary) < 10000;

每个班级名字叫郭志强的数量

4.工资在5000到8000之间的员工的姓名及年龄

select name,age,salary from employee where salary between 5000 and 8000; 

5.雇佣日期在2018年之前的员工信息

select * from employee where hire_date < "2010-01-01";

6.年龄大于20岁的员工信息，从第二条起显示3条

select * from employee where age>20 limit 1,3;

7.按每个部门的平均工资降序排列，显示平均工资

select * from employee where age>20 limit 1,3;