我尝试在db中插入值，但不使用axaj，jquery在value中插入值

Question

我尝试在db

中插入值

$cn = mysqli_connect("localhost","root","","testajax") or die("Opps some thing went wrong");
if(isset($_POST['bottonsave']))
{
    $sql = "insert into tableajax (studentname,gender,phone) values ('{$_POST[studentname]}','{$_POST[gender]}','{$_POST[phone]}')";
    $result = mysqli_query($cn,$sql);
    if($result == false)
    {
        echo 'error - ';
        echo mysqli_error($cn);
    }
    else
    {
        echo "all good'";
    }
}

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>

    <div id ="testforajax">
         <tr>
               <td>StudentName </td>
               <td>:</td>
               <td><input type ="text" id ="studentname" name ="studentname" >
               </td>
               </tr>

                <tr>
               <td>gender </td>
               <td>:</td>
               <td><input type ="text" id ="gender" name ="gender" >
               </td>
               </tr>

                <tr>
               <td>Phone </td>
               <td>:</td>
               <td><input type ="text" id ="Phone" name ="Phone" >
               </td>
               </tr>

                 <input type="button" value ="save" id ="save">
                 </div>
      <script type="text/javascript">
     $(function(){
        // create ajax insert record
        $("#save").click(function(){

        var namestudent = $('#studentname').val();
        var genderstudent  = $('#gender').val();
        var phonestudent = $('#phone').val();
        $.ajax({
                url : "index.php",
                type: "POST",
                async: false,
                data: {
                       buttonsave : 1,
                       studentname : namestudent,
                       gender : genderstudent,
                       phone : phonestudent
                },
                success: function(result)
                {
                    alert("success");
                }
              });

        });
    });

 </script>