#外连接
use girls;
select b1.*,b2.*
from beauty b1
left outer join boys b2
on b1.boyfriend_id = b2.id;
use girls;
select b1.*,b2.*
from beauty b1
right outer join boys b2
on b1.boyfriend_id = b2.id;
select b1.*
from beauty b1
left outer join boys b2
on b1.boyfriend_id = b2.id
where boyName is null;
use girls;
select b1.*,b2.*
from beauty b1
left join boys b2
on b1.boyfriend_id = b2.id
where b1.id > 3;
use myemployees;
select city,department_name
from locations l
left join departments d
on l.location_id = d.location_id
where d.department_id is null;
select e.*,department_name
from employees e
left join departments d
on e.department_id = d.department_id
where department_name in('SAL','IT');