select shiname,shengname from (city left outer join province on  city.shengid=province.id)

select shiname,shengname from (province right outer join city on  city.shengid=province.id)

上面2条语句 执行的结果集一样

 

然而使用下面的语句返回的结果集跟上面不一样

select province.shengname,city.shiname from city, province where  city.shengid=province.id order by province.shengname