[打卡]W-多表查询

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

-- 多表查询分类{归纳式}
--  1、等值链接 vs 非等值连接 
--  2、自连接{自我引用} vs 非自我连接
--  3、内连接 vs 外连接 

-- 1
select * from job_grades;

select e.last_name,e.salary,j.grade_level 
from employees e,job_grades j
where e.salary 
between j.lowest_sal 
and j.highest_sal;

select e.last_name,e.salary,j.grade_level 
from employees e,job_grades j
where e.salary >= j.lowest_sal 
and e.salary <= j.highest_sal;

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;