选择选项菜单从MySQL获取并处理其值

Question

我有从MySQL读取的选择选项菜单。 用户将在选择用户名之前选择成绩。用户从部分选项中选择用户名，而不是从键盘输入用户名。我完成了表单选择选项。但是我无法处理“用户”部分的值。我该如何处理并放入。

<input type="text" required autocomplete="off" name="user"/> 

我的选择选项代码：

   <script>
       window.load=$( document ).ready(function() { 
     $.ajax({
                type:'POST',
                url:'get_class.php',
                success:function(html){
                    $('#Grade').html(html);                
                                      }
                   });             
                    });                     
                   $( document ).ready(function() {

                       $('#Grade').on('change',function(){//change function on Grade to display all user 
        var GradeID = $(this).val();
        if(GradeID){
            $.ajax({
                type:'POST',
                url:'ajaxData.php',
                data:'Grade_id='+GradeID,
                success:function(html){
                    $('#user').html(html);                   
                                      }
                   }); 
                      }else{
                           $('#user').html('<option value="">Select Grade first</option>');

                           }
    }); 
    });

                   </script>

</head>
       <p id="profile1" style="color:red;margin-left:700px;margin-top:100px">
       <b>Examples</b></p><br>
<div class="row">
          <div class="col-md-1 col-sm-12" id="lable1"></div>

                     <div class="col-md-1 col-sm-12" id="lable1"><id="lable1">Grade</div>

                    <div class="col-md-2">

                    <select name="Grade" id="Grade"   
                    data-live-search="true" class="chosen selectpicker form-control" required>
                    <option value="">Select Grade</option>                  
                    </select>
                    </div>
                    <div class="col-md-1 col-sm-12" id="lable1"><id="lable1">user</div>
                    <div class="col-md-2">
                    <select class="selectpicker form-control" name="user" id="user"  autofocus="autofocus" required>
                        <option value="">Select an Option</option>                            
                    </select>        
                    </div>

                  </div>
                    </br>
                    </div>
                    </div>