我有以下代码：

if(mail($to, $subject, $message, $headers)){
    $insert_member_sql = "INSERT INTO members (id, username) VALUES('$id', '$username')";
    $insert_member_res = mysqli_query($con, $insert_member_sql);
    if(mysqli_affected_rows($con, $insert_member_res)>0){
    echo "1";
    }else{
    echo "0";
    }
};

所有人都可以正常发送电子邮件并将信息插入数据库，但是mysqli_affected_rows无法正常工作-如何在运行查询后编辑此代码以回显1？