作业：
1. 查看岗位是teacher的员工姓名、年龄
2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
3. 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资
4. 查看岗位描述不为NULL的员工信息
5. 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资
6. 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
7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪
//1. 查看岗位是teacher的员工姓名、年龄
select name, age from staff_info where state = 'teacher'
//2. 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 state = 'teacher' and age > 30
//3. 查看岗位是teacher且薪资在9000-10000范围内的员工姓名、年龄、薪资
select name, age, salary from staff_info where state = 'teacher' and salary between 9000 and 10000
//4. 查看岗位描述不为NULL的员工信息
select * from staff_info where state_desc is not null
//5. 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 state = 'teacher' and salary in (10000, 9000, 30000)
//6. 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 state = 'teacher' and salary not in (10000, 9000, 30000)
//7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪
select name, annual_salary from staff_info where state = 'teacher' and name like 'jin%'