Oracle的各种连接方法
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          3


sec@ora10g> select * from b;

         A          D          E
---------- ---------- ----------
         1          4          4
         2          5          5
         4          6          6

2. 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          5

3.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 &n