理解Oracle的各种连接方法的最有效的方法就是“躬亲”，在实践中去深刻理解内连接，左外连接，右外连接，全外连接的概念的和效果。1.创建测试表并准备测试数据sec@ora10g> create table a (a number(1),b number(1),c number(1));sec@ora10g> create table b (a number(1),d number(1),e number(1));sec@ora10g> insert into a values(1,1,1);sec@ora10g> insert into a values(2,2,2);sec@ora10g> insert into a values(3,3,3);sec@ora10g> insert into b values(1,4,4);sec@ora10g> insert into b values(2,5,5);sec@ora10g> insert into b values(4,6,6);sec@ora10g> commit;sec@ora10g> select * from a; A B C---------- ---------- ---------- 1 1 1 2 2 2 3 3 3sec@ora10g> select * from b; A D E---------- ---------- ---------- 1 4 4 2 5 5 4 6 62. 内连接sec@ora10g> select * from a, b where a.a=b.a;另外一种写法如下sec@ora10g> select * from a inner join b on a.a=b.a; A B C A D E---------- ---------- ---------- ---------- ---------- ---------- 1 1 1 1 4 4 2 2 2 2 5 53.左外连接sec@ora10g> select * from a,b where a.a=b.a(+);另外一种写法如下sec@ora10g> select * from a left outer join b on a.a=b.a; A B C A D E---------- ---------- ---------- ---------- ---------- ---------- 1 1 1 1 4 4 2 2 2 2 5 5 3 3 34.右外连接sec@ora10g> select * from a,b where a.a(+)=b.a;另外一种写法如下sec@ora10g> select * from a right outer join b on a.a=b.a; A B C A D E---------- ---------- ---------- ---------- ---------- ---------- 1 1 1 1 4 4 2 2 2 2 5 5 4 6 65.全外连接sec@ora10g> select * from a full outer join b on a.a=b.a; A B C A D E---------- ---------- ---------- ---------- ---------- ---------- 1 1 1 1 4 4 2 2 2 2 5 5 3 3 3 4 6 66.小结通过使用Oracle提供的各种SQL连接功能可以解决诸多的“疑难杂症”，需灵活掌握。Good luck.
本文转自My_King1 51CTO博客，原文链接：http://blog.51cto.com/apprentice/1360615，如需转载请自行联系原作者
