如何在PHP文件中检查在表单中提交并通过AJAX调用发送的值

我想做一个INSERT查询在我的php文件的用户被放入组#3。我知道PHP可以检查按钮是否按下或是否设置了某些内容，但如何检查AJAX发送和传递的值呢?

因此，假设我将组级别更改为3(组级别是通过表单中的value选项确定的)。我如何使我的查询检查已选择的选项?

形式

<div class="change_group_button"> 
 <a class="change_group" href="javascript:void(0)">Change User 
Permission</a>
</div><br>
<div id="light" class="change_group_popup">
    <a class="close" href="javascript:void(0)">Close</a>
 <div class="group_success" style="color: red;"></div><br>
    <form id="update_group" action="" method="POST" accept-charset="utf-8">
       <div class="field">
        <label for="group">Group</label>
        <input type="hidden" value="<?php echo $approved_id; ?>" id="approved_id" name="id" />
        <input type="hidden" value="<?php echo $approved_firstname; ?>" id="approved_firstname" name="firstname" />
        <input type="hidden" value="<?php echo $approved_lastname; ?>" id="approved_lastname" name="lastname" />
        <input type="hidden" value="<?php echo $approved_username; ?>" id="approved_username" name="username" />
        <input type="hidden" value="<?php echo $approved_email; ?>" id="approved_email" name="email" />
        <select id='group_id' name='group' required>
            <option value=''><?php echo htmlentities($group); ?></option>
            <option value="1">Bench</option>
            <option value="2">Spectator</option>
            <option value="3">Team Member</option>
            <option value="4">Commissioner</option>
        </select>
    </div>
    <input type="submit" value="submit" name="group">
    </form>

AJAX调用

$('#update_group').on('submit', function (event) {
    event.preventDefault();
        $.ajax({
            url: 'user_group_update.php',
            type: 'POST',
            data: {
            id: $("#approved_id").val(), //id
            firstname: $("#approved_firstname").val(), //firstname
            lastname: $("#approved_lastname").val(), //lastname
            username: $("#approved_username").val(), //username
            email: $("#approved_email").val(), //email
           // update_group: $("#group_id").val() //group level
          update_group: $(this).find( "#group_id option:selected" ).val()
        },
            success: function (data) {
                //do something with the data that got returned
                $(".group_success").fadeIn();
                $(".group_success").show();
                $('.group_success').html('User Permission Level Changed!');
                $('.group_success').delay(5000).fadeOut(400);
                alert(data);
            },
             error: function(jqXHR, textStatus,errorThrown )
            {
              // alert on an http error 
              alert( textStatus +  errorThrown );
            }
        });
        return false;
    });

在我的PHP文件中，我从表单.

中获得这些字段

$approved_id = $_POST['id'];
//test - delete if it doesn't work
$approved_firstname = $_POST['firstname'];
$approved_lastname = $_POST['lastname'];
$approved_username = $_POST['username'];
$approved_email = $_POST['email'];
$change_group = $_POST['update_group'];

$approved_id = $_POST['id'];
if($approved_id == '3')
{
    //do something
}
else
{
    //do something else
}
//test - delete if it doesn't work
$approved_firstname = $_POST['firstname'];
$approved_lastname = $_POST['lastname'];
$approved_username = $_POST['username'];
$approved_email = $_POST['email'];
$change_group = $_POST['update_group'];

if ( $_SERVER['REQUEST_METHOD'] == 'POST' && !empty($_POST) ) {}

if(!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
   // your code
}

$this->input->is_ajax_request();