求一连接查询
表A
id     value
1         4
2         5

表B
id     value
1         6
3         7

需要的结果表
id     a.value     b.value
1         4                 6
2         5              
3                           7

------解决方案--------------------
SQL> create table a(id number,value number);

Table created

SQL> create table b(id number,value number);

Table created

SQL> insert into a values(1,4);

1 row inserted

SQL> insert into a values(2,5);

1 row inserted

SQL> insert into b values(1,6);

1 row inserted

SQL> insert into b values(3,7);

1 row inserted

SQL> select a.id,a.value,b.value from a left join b on a.id = b.id
2 union
3 select b.id,a.value,b.value from b left join a on b.id = a.id
4 ;

ID VALUE VALUE
---------- ---------- ----------
1 4 6
2 5
3 7

SQL>
------解决方案--------------------
明显的全外连接的用法：
给你个例子：
LOVE2008> select * from t;

ID NAME
---------- --------------------
1 WZK
2 ZX
3 wz

LOVE2008> select * from test;

ID VALUE
---------- ----------
1 1
2 2

LOVE2008> select nvl(a.id,b.id),a.value,b.name from test a full outer join t b on a.id=b.id;

NVL(A.ID,B.ID) VALUE NAME
-------------- ---------- --------------------
1 1 WZK
2 2 ZX
3 wz
------解决方案--------------------
love_2008(love2008) 的说法正确，外连接的写法 full join on