mysql的函数 时间戳转时间 手机号中间四位xxx

$waiterData = Db::name('user u')
                        ->field('u.*,g.name gname,FROM_UNIXTIME(u.ctime, "%Y-%m-%d %H:%i:%s") AS dat, insert(u.tel, 4, 4, "XXXX") as mobile')
                        ->field('u.*')
                        ->join('zf_user_group g','g.id = u.gid')
                        ->where($where)
                        ->order("u.id desc")
                        ->page($page,$limit)
                        ->select();