问Ajax脚本不插入数据库

EN

<a href="javascript:;" class="newFriend has-tooltip pull-right" data-title="Add as friend" id="'.$id.'"" ><i class="fa fa-user"></i> Add as friends </a>

include 'database.php';
$pdo = Database::connect(); 

if(!empty($_POST["id"])) {

    $friend_id = $_POST['id'];             
    $id = $_SESSION['id'];   

            $value = $pdo->prepare('SELECT * FROM user_friends WHERE friend_id= ? and id = ?'); // BDD query, page ID values
            $value->bindParam(1, $friend_id, PDO::PARAM_INT);
            $value->bindParam(2, $id, PDO::PARAM_INT);              
            $value->execute();
            $result = $value->fetch();    

if( $result > 0) {
        echo 'already added';           
}
else 
{
    $friend_id = $_POST['id'];             
    $id = $_SESSION['id']; 

    $query = $pdo -> prepare("INSERT INTO user_friends (friend_id, id)
                            VALUES (:friend_id, :id)");   
    $query -> execute(array(
                      ":friend_id"         => $friend_id,
                      ":id"          => $id
    ));     
}

<script>    

$(document).ready(function(){
$('.newFriend', $('.buttons')).click(function(){
    $.post('misc/add_friend.php', 
    { 
        "id": $(this).attr('id'),
    },
    function(data){
        if(data == 0){
            $('#message_newfriend').html('<div id="alertFadeOut" style="color: green">Added as friend!</div>');
             $('#alertFadeOut').fadeOut(3000, function () {
                $('#alertFadeOut').text('');
             }); 
        }
        else {
             $('#message_newfriend').html('<div id="alertFadeOut" style="color: green">User is already in your friend list!</div>');
             $('#alertFadeOut').fadeOut(3000, function () {
                $('#alertFadeOut').text('');
             }); 
        }
     });
});
});
</script>