<?php
$servername = "localhost";
$username = "BAUM";
$password = "HAUS";
$dbname = "BAUMHAUS";

print_r($_POST);

if (isset($_POST['update'])){ // prüfen ob formular übermittelt
   $ID = $_POST['id'];

   if ($ID > 0) {
    // Create connection
    $conn = mysqli_connect($servername, $username, $password, $dbname);
    // Check connection
    if (!$conn)
        die("Connection failed: " . mysqli_connect_error());

    $id = $_POST['id'];
    $title = $_POST['title'];
    $content = $_POST['content'];
    $img = $_POST['img'];
    $img2 = $_POST['img2'];

    if (filter_var($content, FILTER_VALIDATE_EMAIL)) {

        //entweder '$variable' oder '".$variable."' beides möglich liest du aus einem array aus geht nur die zweite variante

        $sql = "UPDATE texte
        SET
        id='".$id."',
        title='".$title."',
        content='".$content."',
        img='".$img."',
        img2='".$img2."',

        WHERE id='$id' LIMIT 1";

        if (mysqli_query($conn, $sql)) {
            echo "Record updated successfully";
        } else {
            echo "Error updating record: " . mysqli_error($conn);
        }
    } else

    mysqli_close($conn);
   } else {
       echo "ID ERROR";
   }

}
?>