小佳

摘要： 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=provi 阅读全文