作业：

1. 查看岗位是teacher的员工姓名、年龄 
select name,age from staff_info where jobs = 'teacher';

1. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
   select name,age from staff_info where jobs = 'teacher' and age > 30;
2. 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资
   select name,age,salary from staff_info where jobs = 'teacher' and salary between 9000 and 10000;
3. 查看岗位描述不为NULL的员工信息
   select * from staff_info where jobs_info is not null;
4. 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资
   select name,age,salary from staff_info where jobs = 'teacher' and salary in(10000,9000,30000);
5. 查看岗位是teacher且薪资不是10000或9000或30000的员工姓名、年龄、薪资
   select name,age,salary from staff_info where jobs = 'teacher' and salary not in(10000,9000,3000);
6. 查看岗位是teacher且名字是jin开头的员工姓名、年薪
   select name,salary from staff_info where jobs = 'teacher' and name like jin%;