How can I update the info from database but without updating image in PHP [closed]

I’m new here. I need to know the problem with these codes since I want to update blog content without image change but I’m stuck with this problem, can you help me to fix my code, please?

if (isset($_POST['edit_blog'])) {
        $title = mysqli_real_escape_string($config, $_POST['blog_title']);
        $body = mysqli_real_escape_string($config, $_POST['blog_body']);
        $filename = $_FILES['blog_image']['name'];
        $tmp_name = $_FILES['blog_image']['tmp_name'];
        $size = $_FILES['blog_image']['size'];
        $image_ext = strtolower(pathinfo($filename, PATHINFO_EXTENSION));
        $allow_type = ['jpg', 'png', 'jpeg'];
        $destination = "upload/".$filename;
        $category = mysqli_real_escape_string($config, $_POST['category']);
        if (!empty($filename)) {
            if (in_array($image_ext, $allow_type)) {
                if ($size <= 2000000) {
                    $unlink = "upload/".$result['blog_image'];
                    unlink($unlink);
                    move_uploaded_file($tmp_name, $destination);
                    $sql3 = "UPDATE blog SET blog_title = '$title', blog_body = '$body', blog_image = '$filename', category = '$category', author_id = '$author_id' WHERE blog_id = '$blogID'";
                    $query3 = mysqli_query($config, $sql3);
                    if($query3) {
                        $msg = ['Update success', 'alert-success'];
                        $_SESSION['msg'] = $msg;
                        header('location:index.php');
                    } else {
                        $msg = ['Failed, try again', 'alert-danger'];
                        $_SESSION['msg'] = $msg;
                        header('location:index.php');
                    }
                } else {
                    $msg = ['Image should be not greater than 2 MB', 'alert-danger'];
                    $_SESSION['msg'] = $msg;
                    header('location:index.php');
                }
            } else {
                $msg = ['This type of image file is not allowed (only jpg, png and jpeg accepted)', 'alert-danger'];
                $_SESSION['msg'] = $msg;
                header('location:index.php');
            }
        } else {
            $sql3 = "UPDATE blog SET blog_title = '$title', blog_body = '$body', category = '$category', author_id = '$author_id' WHERE blog_id = '$blogID'";
            $query3 = mysqli_query($config, $sql3);
            if($query3) {
                $msg = ['Update success', 'alert-success'];
                $_SESSION['msg'] = $msg;
                header('location:index.php');
            } else {
                $msg = ['Failed, try again', 'alert-danger'];
                $_SESSION['msg'] = $msg;
                header('location:index.php');
            }
        }
    }

I need to know the problem of these codes about the update without image change:

else {
$sql3 = “UPDATE blog SET blog_title = ‘$title’, blog_body = ‘$body’, category = ‘$category’, author_id = ‘$author_id’ WHERE blog_id = ‘$blogID'”;
$query3 = mysqli_query($config, $sql3);
if($query3) {
$msg = [‘Update success’, ‘alert-success’];
$_SESSION[‘msg’] = $msg;
header(‘location:index.php’);
} else {
$msg = [‘Failed, try again’, ‘alert-danger’];
$_SESSION[‘msg’] = $msg;
header(‘location:index.php’);
}
}