用PHP打开一个新函数

<div class="btn-group">
        <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
        Frequenza <span class="caret"></span>
        </button>
        <ul class="dropdown-menu" role="menu">
            <?php
                $query_frequenza="SELECT DISTINCT FREQUENZA FROM Dettagli_macchina WHERE  macchine_id='$macchine' and Email='$_SESSION[login_user]'";
                $result=mysqli_query($conne,$query_frequenza);
                while($row=mysqli_fetch_array($result)){
                    $frequenza=$row['FREQUENZA'];
                    echo"<li><a href='#?frequenza=$frequenza' onclick='showfiltro2()'>$frequenza</a></li>";
                }
                ?>
        </ul>
        </div>
<script type = "text/javascript">
            function showfiltro2() {
                document.getElementById("filtro2").style.display = "block";
                document.getElementById("filtro1").style.display = "none";
            }
        </script>
        <div id = "filtro2" style="display:none">
        <?php
            $filtro2=$_GET['frequenza'];
            $query="SELECT DISTINCT * FROM Dettagli_macchina WHERE macchine_id='$macchine' and Email='$_SESSION[login_user]' and FREQUENZA='$filtro2' ";
            $result=mysqli_query($conne,$query);
            echo 'Found '. mysqli_num_rows($result) .'results';
            echo "<table><tr>";
            while ($row = mysqli_fetch_array($result)) {
                echo "<tr><td>";
                echo $row['COMPONENTE'];
                echo "</td>";
                echo "<td>";
                echo $row['DETTAGLIO ATTIVITA'];
                echo "</td>";
                echo "<td>";
                echo $row['FREQUENZA'];
                echo "</td>";
                echo "<td>";
                echo $row['DATA-PREVISTA'];
                echo "</td>";
                echo "</tr>";
                }
            echo"</tr></table>";
            ?>
        </div>

你的问题源于对PHP和HTML如何工作以及数据如何在两者之间流动的误解。

首先，重要的是要记住PHP和HTML是两个完全独立的部分，它们在"请求->回复"链之外不相互交互。
这意味着所有的PHP代码都在服务器上执行，然后客户端才能得到处理的输出。服务器(PHP)不关心输出是什么类型的，也不知道如何解析它;对于PHP来说，这些都是简单的文本。
在PHP代码被完全解析之后，客户机接收到结果文本。然后它注意到它可以将该文本理解为HTML，并将其解析为网页。此时，PHP代码根本不存在于代码中，web浏览器(客户端)对它一无所知。

不幸的是，很多教程都像你上面所做的那样，把PHP和HTML代码混在一起，因为这进一步混淆了两者，使它们看起来像是相互交流的。我建议将所有PHP代码移到html代码之上，并在向浏览器发送任何内容之前完成所有处理。
这不仅会让我们更容易跟踪和理解正在发生的事情及其原因;但它也允许你在代码中添加更多的功能，而不会试图打破物理定律。(例如:在生成表单的过程中，决定不再向用户显示表单。)

所有这些都意味着你不能通过点击来"打开一个功能"。您使用上述单击向服务器发送请求，然后PHP代码检查传入数据中的某些预定条件(get参数等)，然后调用所述条件满足的函数。
换句话说，就像这样:

// First off we should use PDO, as mysql_*() is deprecated and removed in PHP7.
$db = new PDO ($dsn);
// Using prepared statements here, to prevent SQL injections.
$stmt = $db->prepare ("SELECT DISTINCT FREQUENZA FROM Dettagli_macchina WHERE  macchine_id=:machineID and Email=:email");
$data = array (':machineID' => $macchine, ':email' => $_SESSION['login_user']);
if (!$stmt->exec ($data)) {
    // Something went wrong, handle it.
}
// Initialize a variable to hold the generated menu, and a template to use when creating it.
$menuOut = $searchOut = '';
$menuTemplate = "<li><a href='#?frequenza=%s' onclick='showfiltro2()'>%s</a></li>";
// Using prepared statements we can iterate through all of the results with foreach().
foreach ($stmt->fetchAll () as $row) {
    // Using htmlspecialchars() and rawurlescape() to prevent against XSS, and other HTML-injection attacks/mistakes.
    // Notice where and in what order I've used the different functions, as one protects the URL as well.
    $menuOut .= sprintf ($menuTemplate, htmlspecialchars (rawurlencode ($row['FREQUENZA'])), htmlspecialchars ($row['FREQUENZA']));
}
// Since this is probably the "function" you want to execute with said click, this is where we check if it
// has been sent by the client.
if (!empty ($_GET['frequenza'])) {
    // Here you want to check to see if the parameter is actually something you'd expect, and not some random(?) garbage.
    $filtro2 = $_GET['frequenza'];
    // Again, prepared statements as your code was open to SQL injections!
    $query = "SELECT DISTINCT * FROM Dettagli_macchina WHERE macchine_id=:machineID and Email=:email and FREQUENZA=:frequency";;
    $stmt = $db->prepare ($query);
    $data = array (
            ':machineID' => $macchine,
            ':email' => $_SESSION['login_user'],
            ':frequency' => $filtro2);
    if (!$res = $stmt->exec ($data)) {
        // Somethign went wrong with the query, handle it.
    }
    // Initialize a variable to hold the output, and the template to use for generating it.
    $searchOut = '<table>';
    $searchTemplate = '<tr><td>%s</td><td>%s</td><td>%s</td><td>%s</td></tr>';
    $count = 0;
    foreach ($stmt->fetchAll () as $row) {
        // Again, protection against XSS and other HTML-breaking mistakes.
        $searchOut .= sprintf ($searchTemplate,
                htmlspecialchars ($row['COMPONENTE']),
                htmlspecialchars ($row['DETTAGLIO ATTIVITA']),
                htmlspecialchars ($row['FREQUENZA']),
                htmlspecialchars ($row['DATA-PREVISTA']));
    }
    $searchOut = "<p>Found {$count} results</p>{$searchOut}</table>";
}
?>
<div class="btn-group">
    <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
        Frequenza <span class="caret"></span>
        </button>
    <ul class="dropdown-menu" role="menu">
<?php echo $menuOut; ?>
    </ul>
</div>
<script type="text/javascript">
            function showfiltro2() {
                document.getElementById("filtro2").style.display = "block";
                document.getElementById("filtro1").style.display = "none";
            }
        </script>
<div id="filtro2" style="display: none">
    <?php echo $searchOut; ?>
</div>

我添加了一些注释来解释我做了什么和为什么做这些事情，以及从旧的(!)，弃用和过时的mysql_*()函数切换到PDO。
您可以在PHP手册