获取后 %NOTFOUND 可以返回 null 吗?

问题描述

这个问题提出了一个非常有趣的观点；Oracle 文档中关于 %NOTFOUND 在获取后是否可能为空似乎存在矛盾.是吗?

This question raised a very interesting point; there seems to be a contradiction in the Oracle documentation on whether it's possible for %NOTFOUND to be null after a fetch. Is it?

引用 11g 文档

注意:在例 6-16 中，如果 FETCH 从不获取一行，则 c1%NOTFOUND始终为 NULL，并且永远不会退出循环.防止无限循环，请改用此 EXIT 语句:EXIT WHEN c1%NOTFOUND OR(c1%NOTFOUND 为空);

文档似乎直接自相矛盾，因为它还说明了以下内容，这意味着在获取后 %NOTFOUND cannot 为 null.

The documentation seems to directly contradict itself as it also says the following, which implies that after a fetch %NOTFOUND cannot be null.

%NOTFOUND(%FOUND 的逻辑相反)返回:
在显式游标打开之后但在第一次获取之前为 NULL
如果最近从显式游标中获取的数据返回了一行，则为 FALSE
否则为真

10g 文档类似的警告，这不一定是直接矛盾，因为它警告可能无法成功执行获取以显示此行为.

The 10g documentation has a similar warning, which isn't, necessarily, a direct contradiction as it warns that a fetch might not execute successfully in order for this behaviour to be exhibited.

在第一次获取之前，%NOTFOUND 评估为 NULL.如果 FETCH 从不成功执行，EXIT WHEN 条件从不为 TRUE，并且循环永远不会退出.为了安全起见，您可能需要使用以下内容改为退出语句:

当 c1%NOTFOUND 或 c1%NOTFOUND 为空时退出；

EXIT WHEN c1%NOTFOUND OR c1%NOTFOUND IS NULL;

在什么情况下获取可能失败"或在执行获取后 %NOTFOUND 可能返回 null?

In what situations might a fetch either "fail" or might %NOTFOUND return null after a fetch has been executed?

推荐答案

我可以找到一个 fetch 可能失败的情况:

I can find a situation where a fetch can fail:

declare
  i integer;
  cursor c is
    select 1 / 0 from dual;
begin
  open c;

  begin
    fetch c
      into i;
  exception
    when others then
      dbms_output.put_line('ex');
  end;

  if c%notfound is null then
    dbms_output.put_line('null');
  elsif c%notfound then
    dbms_output.put_line('true');
  else
    dbms_output.put_line('false');
  end if;
  close c;

end;

但这只会让你的问题更强烈，因为它会评估为空，无论是在 10g 还是 11g ...

But this only makes your question stronger since it will evaluate to null, neither in 10g nor in 11g ...

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