Oracle PL/SQL之IN OUT NOCOPY

最新推荐文章于 2021-04-16 09:39:20 发布

原创最新推荐文章于 2021-04-16 09:39:20 发布 · 3.3k 阅读

2 ·

CC 4.0 BY-SA版权

文章标签：

#oracle #parameters #collections #exception #reference #application

Oracle - PL/SQL 专栏收录该内容

58 篇文章

订阅专栏

本文探讨了子程序中IN、OUT及INOUT参数的传递机制。IN参数通过引用传递，OUT和INOUT参数默认按值传递。文章还介绍了NOCOPY提示如何改变这一行为，并通过示例代码展示了不同情况下的参数值变化。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Suppose a subprogram declares an IN parameter, an OUT parameter, and an IN OUT parameter. When you call the subprogram, the IN parameter is passed by reference. That is, a pointer to the IN actual parameter is passed to the corresponding formal parameter. So, both parameters reference the same memory location, which holds the value of the actual parameter.

By default, the OUT and IN OUT parameters are passed by value. That is, the value of the IN OUT actual parameter is copied into the corresponding formal parameter. Then, if the subprogram exits normally, the values assigned to the OUT and IN OUT formal parameters are copied into the corresponding actual parameters.

当我们声明一个参数是IN类型时，进行传参是将传给该参数一个实参的指针；

当我们声明一个参数是OUT或者IN OUT类型时，进行传参是将传给该参数一个实参的拷贝；

只有当程序正常结束时，赋给OUT或者IN OUT类型参数的值才会返回（除非使用了NOCOPY）。

将NOCOPY应用在传递数据量很大的参数（such as collections, records, and instances of object types）时，可起到优化性能的作用。

当参数是OUT或者IN OUT类型时：没有NOCOPY＝按值传递（ByVal）；加上NOCOPY＝按引用传递（ByRef）。

Test Code:

DECLARE l_1 NUMBER := 10; l_2 NUMBER := 20; l_3 NUMBER := 30; PROCEDURE test_out ( p1 IN NUMBER ,x1 IN OUT NUMBER ,x2 IN OUT NOCOPY NUMBER ) IS BEGIN x1 := p1; dbms_output.put_line('inside test_out, x1=' || x1); x2 := p1; dbms_output.put_line('inside test_out, x2=' || x2); raise_application_error(-20001, 'test NOCOPY'); END; BEGIN dbms_output.put_line('before, l_1=' || l_1 || ', l_2=' || l_2 || ', l_3=' || l_3); BEGIN --the OUT parameter has no value at all until the program terminates successfully, --unless you have requested use of the NOCOPY hint test_out(l_1, l_2, l_3); EXCEPTION WHEN OTHERS THEN dbms_output.put_line('SQLCODE => ' || SQLCODE || ', SQLERRM => ' || SQLERRM); END; dbms_output.put_line('after, l_1=' || l_1 || ', l_2=' || l_2 || ', l_3=' || l_3); END;

Output:

before, l_1=10, l_2=20, l_3=30 inside test_out, x1=10 inside test_out, x2=10 SQLCODE => -20001, SQLERRM => ORA-20001: test NOCOPY after, l_1=10, l_2=20, l_3=10

Ref:

http://download.oracle.com/docs/cd/B10500_01/appdev.920/a96624/08_subs.htm#12813