我怎么知道Perl DBI查询返回多少行? [英] How do I know how many rows a Perl DBI query returns?

问题描述

我基本上试图使用Perl在数据库中进行搜索，以判断是否存在具有特定ID的项目.此搜索不能返回任何行，但是也可以返回一个行.

I'm trying to basically do a search through the database with Perl to tell if there is an item with a certain ID. This search can return no rows, but it can also return one.

我有以下代码:

my $th = $dbh->prepare(qq{SELECT bi_exim_id FROM bounce_info WHERE bi_exim_id = '$exid'});
$th->execute();
if ($th->fetch()->[0] != $exid) {
        ...

基本上，这将尝试查看是否返回了ID，如果没有返回，请继续执行脚本.但是它在$th->fetch()->[0]上引发了Null数组引用错误. 我怎样才能简单地检查它是否返回行还是现在?

Basically, this tries to see if the ID was returned and if it's not, continue with the script. But it is throwing a Null array reference error on the $th->fetch()->[0] thing. How can i just simply check to see if it returned rows or now?

推荐答案

my $th = $dbh->prepare(qq{SELECT bi_exim_id FROM bounce_info WHERE bi_exim_id = '$exid'});
$th->execute();
my $found = 0;
while ($th->fetch()) 
{
   $found = 1;
}

如果该行不存在，您的查询将不会返回任何内容，因此您无法取消对提取的引用.

Your query won't return anything if the row doesn't exist, so you can't de-reference the fetch.

更新:您可能希望将其重写为

Update: you might want to re-write that as

my $found = $th->fetch();

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