存储过程参数是timestamp，怎么加小数位数定义？

benh

想在存储过程的参数timestamp定义为非默认6位小数长度的，可是遇到下面问题，请大家帮忙看看。

SQL> create or replace procedure SP_TS_IO(arg in out timestamp() as
  2  begin
  3  update sp set ts=arg where param='I';
  4  select ts into arg from sp where param='O';
  5  commit;
  6  end;
  7  /

Warning: Procedure created with compilation errors.

SQL> show errors;
Errors for PROCEDURE SP_TS_IO:

LINE/COL ERROR
-------- -----------------------------------------------------------------
1/40     PLS-00103: Encountered the symbol "(" when expecting one of the
         following:
         := . ) , @ % with default character
         The symbol ":=" was substituted for "(" to continue.

benh

SQL> create or replace procedure SP_TS_IO(arg in out timestamp( 8 ) ) as
  2  begin
  3  update sp set ts=arg where param='I';
  4  select ts into arg from sp where param='O';
  5  commit;
  6  end;
  7  /

Warning: Procedure created with compilation errors.

SQL> show errors;
Errors for PROCEDURE SP_TS_IO:

LINE/COL ERROR
-------- -----------------------------------------------------------------
1/40     PLS-00103: Encountered the symbol "(" when expecting one of the
         following:
         := . ) , @ % with default character
         The symbol ":=" was substituted for "(" to continue.