[打卡]甄帅垚---多表查询

#查询员工id和部门名字

select employee_id,last_name from employees,departments where employees.department_id =departments.department_id;

#角度三：内连接vs外连接

SELECT * FROM EMPLOYEES;
# 外连接的分类：左外连接，右外连接 满外连接。
#mysql不支持外连接
select employee_id,last_name from employees,departments where employees.department_id =departments.department_id(+);

select employee_id, department_name,city
from employees e join departments d
on e.department_id=d.department_id
join locations l
on d.location_id=l.location_id;

select employee_id,department_name
from employees e left join departments d
on e.department_id = d.department_id;

select employee_id,department_name
from employees e right join departments d
on e.department_id = d.department_id;