plsql的參數IN和OUT

代碼片段一

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;

調用

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;

 

結果

bumon1,ING
,ING
bumon1,after
,after

當參數類型是OUT的情況下，原來record（v_dept)中的值也沒有了。如果是IN OUT的情況下，原來record的值還保持了原來的樣子。

當然根據實際情況使用的時候設置就可以了，但是如果是預想某種情況下就重新設定值，不滿足條件就什么也不做，原值不變的話，寫成OUT就錯了。

關於oracle的參數的值傳遞，還是引用傳遞，官方是這么解釋的。

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