内连接，外连接的转换

# select e.last_name,e.first_name,d.dept_no
# from employees e 
# inner join dept_emp d
# on e.emp_no=d.emp_no;

select e.last_name,e.first_name,d.dept_no
from employees e 
left join dept_emp d
on e.emp_no=d.emp_no
where d.dept_no is not null;

备忘