检查空结果(PHP、PDO 和 MySQL)

Checking for an empty result (PHP, PDO, and MySQL)(检查空结果(PHP、PDO 和 MySQL))

问题描述

我在这里做错了什么?我只是从表中检索结果，然后将它们添加到数组中.一切都按预期工作，直到我检查结果为空...

What am I doing wrong here? I'm simply retrieving results from a table and then adding them to an array. Everything works as expected until I check for an empty result...

这会得到匹配项，将其添加到我的数组中并按预期回显结果:

This gets the match, adds it to my array and echoes the result as expected:

$today = date('Y-m-d', strtotime('now'));

$sth = $db->prepare("SELECT id_email FROM db WHERE hardcopy = '1' AND hardcopy_date <= :today AND hardcopy_sent = '0' ORDER BY id_email ASC");

$sth->bindParam(':today', $today, PDO::PARAM_STR);

if(!$sth->execute()) {
    $db = null;
    exit();
}

while ($row = $sth->fetch(PDO::FETCH_ASSOC)) {
    $this->id_email[] = $row['id_email'];
    echo $row['id_email'];
}

$db = null;
return true;

当我尝试检查空结果时，我的代码返回空"，但不再产生匹配的结果:

When I try to check for an empty result, my code returns 'empty', but no longer yields the matching result:

$today = date('Y-m-d', strtotime('now'));

$sth = $db->prepare("SELECT id_email FROM db WHERE hardcopy = '1' AND hardcopy_date <= :today AND hardcopy_sent = '0' ORDER BY id_email ASC");

$sth->bindParam(':today',$today, PDO::PARAM_STR);

if(!$sth->execute()) {
    $db = null;
    exit();
}

if ($sth->fetchColumn()) {
    echo 'not empty';
    while ($row = $sth->fetch(PDO::FETCH_ASSOC)) {
        $this->id_email[] = $row['id_email'];
        echo $row['id_email'];
    }
    $db = null;
    return true;
}
echo 'empty';
$db = null;
return false;

推荐答案

当您执行 $sth->fetchColumn() 时，您将丢弃结果行.这不是您检查是否有任何结果的方式.你做

You're throwing away a result row when you do $sth->fetchColumn(). That's not how you check if there are any results. You do

if ($sth->rowCount() > 0) {
  ... got results ...
} else {
   echo 'nothing';
}

相关文档在这里:PDOStatement::rowCount

Relevant documentation is here: PDOStatement::rowCount

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