我在将新发布的数据附加到现有数据时遇到问题。
现在，当单击submit按钮时，它将仅用$header和新的$u post[“notes”]值覆盖“notes”的现有值。
我希望它做的是：$header+$\u post[“notes”]+$notes（现有数据）
这是我目前的代码：

<?php
    // Database connection file
    include_once("../config.php");

    // Get id from url
    $id = $_GET['id'];

    // Selecting data associated with this id
    $sql = "SELECT * FROM testtable WHERE id=:id";
    $query = $dbConn->prepare($sql);
    $query->execute(array(':id' => $id));

    while($row = $query->fetch(PDO::FETCH_ASSOC)){
        $notes = $row['notes'];
    }
?>

<?php
        // Create Header
        $header = "----- Updated on " . date("Y-m-d") . " at " . date("h:i:sa") . " ----- <br>";
        // Current note data
        $currentnotes = $notes;
        // Append Header + Post + Current Data
        $appendednotes = $header;
        $appendednotes .= $_POST["notes"];
        $appendednotes .= "<br>";
        $appendednotes .= $currentnotes;

    if(isset($_POST['update'])){
        $id = $_POST['id'];
        $notes=$appendednotes;

        // Update the table
        $sql = "UPDATE testtable SET
            notes=:notes
        WHERE id=:id";

        $query = $dbConn->prepare($sql);
    
        $query->bindparam(':id', $id);
        $query->bindparam(':notes', $notes);

        $query->execute();

        // Redirect to the display page
        header("Location: index.php");
        
    }
?>

这是找到我想要做的事情的最接近的例子，但是我不确定如何调整它：php post to variable，然后append to txt