[打卡]甄帅垚

select employee_id,last_name,department_name,city 
from employees,departments,locations 
where employees.department_id=departments.department_id and
departments.location_id=locations.location_id;

/*

演绎式：发现提出一个问题----解决一个问题---发现提出第二个问题------解决第二问题---


*/

#多表查询的分类用的是归纳式

/*
角度1：等值链接 VS 非等值链接
角度2：自连接 （自我引用） VS  妃子链接
角度3： 内连接 VS 外连接  

*/
select * from job_grades ;

#查询名字，月薪和对应的等级
#between and 
select last_name ,salary , grade_level
from employees e, job_grades j
where e.salary between j.lowest_sal and j.highest_sal;
# 区间[]
select last_name ,salary , grade_level
from employees e, job_grades j
where e.salary >= j.lowest_sal and e.salary <= j.highest_sal;

#角度二：自连接  VS非自连接
select * from employees;
select emp.employee_id,emp.last_name, mgr.employee_id,mgr.last_name
from employees emp, employees mgr
where emp.manager_id= mgr.employee_id;