plsql的参数IN和OUT

代码片段一

create or replace procedure scott.pro_para_inout(p_dname in out scott.dept.dname%TYPE, 
                                           p_loc out scott.dept.loc%TYPE) is
begin
  dbms_output.put_line(p_dname || ',ING');
  dbms_output.put_line(p_loc || ',ING' );
end pro_para_inout;

调用

DECLARE
  v_dept scott.dept%ROWTYPE;
  
BEGIN
  
  v_dept.dname :='bumon1';
  v_dept.loc :='SH';
  
  -- Call the procedure
  scott.pro_para_inout(v_dept.dname, v_dept.loc);
  
  dbms_output.put_line(v_dept.dname || ',after');
  dbms_output.put_line(v_dept.loc || ',after');
end;

结果

bumon1,ING
,ING
bumon1,after
,after

当参数类型是OUT的情况下，原来record（v_dept)中的值也没有了。如果是IN OUT的情况下，原来record的值还保持了原来的样子。

当然根据实际情况使用的时候设置就可以了，但是如果是预想某种情况下就重新设定值，不满足条件就什么也不做，原值不变的话，写成OUT就错了。

关于oracle的参数的值传递，还是引用传递，官方是这么解释的。

Summary of Subprogram Parameter Modes

Table 8-1 summarizes the characteristics of parameter modes.

Table 8-1 Parameter Modes

IN	OUT	IN OUT
The default	Must be specified	Must be specified
Passes a value to the subprogram	Returns a value to the caller	Passes an initial value to the subprogram and returns an updated value to the caller
Formal parameter acts like a constant	Formal parameter acts like an uninitialized variable	Formal parameter acts like an initialized variable
Formal parameter cannot be assigned a value	Formal parameter must be assigned a value	Formal parameter should be assigned a value
Actual parameter can be a constant, initialized variable, literal, or expression	Actual parameter must be a variable	Actual parameter must be a variable
Actual parameter is passed by reference (the caller passes the subprogram a pointer to the value)	Actual parameter is passed by value (the subprogram passes the caller a copy of the value) unless NOCOPY is specified	Actual parameter is passed by value (the caller passes the subprogram a copy of the value and the subprogram passes the caller a copy of the value) unless NOCOPY is specified