SQL> create table a("1" varchar2(10),"2" varchar2(10),"3" varchar2(10));

表已创建。

SQL> create table b("1" varchar2(10),"4" varchar2(10), "5" varchar2(10));

表已创建。

SQL> create table c("4" varchar2(10),"6" varchar2(10), "7" varchar2(10));

表已创建。

SQL> insert into a values('a1','b1','c1');

已创建 1 行。

SQL> insert into a values('a2','b2','c2');

已创建 1 行。

SQL> insert into b values('a1','d1','e1');

已创建 1 行。

SQL> insert into c values('d1','f1','g1');

已创建 1 行。

SQL> select m.a,l.g from
  2  (select 1 as a, 2 as b ,3 as c from a)m ,
  3  (select 1 as a, 4 as e ,5 as f from b)n ,
  4  (select 4 as e, 6 as g ,7 as h from c)l
  5    where m.a(+)=n.a and n.e=l.e;

         A          G
---------- ----------
         1          6
         1          6