如何将 oracle 过程的参数默认设置为选择的结果？
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How can I set an oracle procedure's parameter default to the result of a select?
提问by JerryKur
I have an oracle Procedure and I want to set the default parameter to the result of a select statement such as below.
我有一个 oracle 过程，我想将默认参数设置为如下所示的 select 语句的结果。
procedure foo( startID number : = max(x.id) from xtable x )
but the code above is illegal syntax.
但上面的代码是非法的语法。
回答by Vincent Malgrat
You can use an otherwise unvalid value for this meaning, for example NULL:
您可以为此含义使用其他无效值，例如 NULL：
PROCEDURE foo (p_id NUMBER DEFAULT NULL) IS
l_startID NUMBER := p_id;
BEGIN
IF p_id IS NULL THEN
SELECT max(id) INTO l_startID FROM xtable;
END IF;
...
END;
If your function/procedure is in a package, you could also overloadit:
如果你的函数/过程在一个包中，你也可以重载它：
PROCEDURE foo (p_id NUMBER)
[...]
PROCEDURE foo IS
l_startID NUMBER;
BEGIN
SELECT max(id) INTO l_startID FROM xtable;
foo(l_startID);
END;
