问在数据库中插入数据时没有结果吗？

EN

<form action="index.php?type=add_lesson&type=add" method="post">
                <?php echo $lesson_title; ?><br/><input type="text" name="title" style="width:450px;" /><br/>
                <?php echo $lesson_url; ?><br/><input type="text" name="url" style="width:450px;" /><br/>
                <?php echo $keywords; ?><br/><input type="text" name="kewyords" style="width:450px;" />
                    <br/><br/><br/>
                    <input type="submit" value="<?php echo $submit;?>" class="button"  /></form>

if($_GET['type'] == "add_lesson"){
        include_once(fls."add_lesson.php");
    }

if($_GET['type'] == 'add'){
    $title    = htmlspecialchars($_POST['title']);
    $url      = htmlspecialchars($_POST['url']);
    $kewyords = htmlspecialchars($_POST['kewyords']);
        $sql = $mysqli->query("INSERT INTO LESSONS(L_TITLE,L_URL,L_COMMENTS,L_VIEWS,L_KEYWORDS)
                                VALUES('".$title."','".$url."','0','0','".$kewords."') ");
        echo $added_sucessfully;
}