内连接：106(106, 11)
select e.last_name, d.department_name
from employees e, departments d
where e.department_id=d.department_id;
select e.last_name, d.department_name
from employees e join departments d on e.department_id=d.department_id; inside
左外连接：107（106+1）
select e.last_name, d.department_name
from employees e, departments d
where e.department_id=d.department_id(+);
select e.last_name, d.department_name
from departments d, employees e
where e.department_id=d.department_id(+);
select e.last_name, d.department_name
from employees e left outer join departments d
on e.department_id=d.department_id;
右外连接：122（106+16）
select e.last_name, d.department_name
from employees e, departments d
where e.department_id(+)=d.department_id;
select e.last_name, d.department_name
from employees e right outer join departments d
on e.department_id=d.department_id;
完全外连接：123（106+1+16）
select e.last_name, d.department_name
from employees e full outer join departments d
on e.department_id=d.department_id;
多表连接的扩展：
n张表连接：
select e.last_name, d.department_name, l.city
from employees e, departments d, locations l
where e.department_id=d.department_id
and d.location_id=l.location_id;
select e.last_name, d.department_name, l.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 e.last_name, d.department_name, l.city
from employees e, departments d, locations l
where e.department_id=d.department_id(+)
and d.location_id=l.location_id(+);
select e.last_name, d.department_name, l.city
from employees e left outer join departments d on e.department_id=d.department_id
left outer join locations l on d.location_id=l.location_id;