求教进出库的问题
数据表结构
--------------------------------------------
number              type             t_id
--------------------------------------------
54                   1                 12
30                   2                 13
68                   1                 13
---------------------------------------------

type中 1代表 进了多少，2代表出了多少 

现在想要实现的结果如下：
---------------------------------------------
t_id            进                     出           
--------------------------------------------
12              54                 0
13              68                 30
--------------------------------------------------
求解
------解决方案--------------------

SQL> select * from test;



         N          T         ID

---------- ---------- ----------

        54          1         12

        30          2         13

        68          1         13



SQL> select id,sum(n * decode(t,1,1,0)) as "in",

  2          sum(n * decode(t,2,1,0)) as "out"

  3  from test group by id;



        ID         in        out

---------- ---------- ----------

        13         68         30