如何使用循环检查用户IP进行注册

我的网络检查用户IP是否注册了这部分代码：

$userip=check_ip_behind_proxy();
//get today date
$today = date('Y-m-d',time());
//get yesterday date
$days_ago = date('Y-m-d', mktime(0, 0, 0, date("m") , date("d") - 1, date("Y")));
//Get number of IP coincidences of registering user within logged in users YESTERDAY And TODAY 
$already_reg=$db->get_var("SELECT COUNT(*) FROM `prefix_users` WHERE `user_lastlogin` like '%$today%' AND user_lastip = '$userip'");
$already_reg2=$db->get_var("SELECT COUNT(*) FROM `prefix_users` WHERE `user_lastlogin` like '%$days_ago%' AND user_lastip = '$userip'");
//if there is coincidence, no register allowed for that IP - he already has an account!
if ($already_reg >= 1){
        $form_username_error[] = $main_smarty->get_config_vars('Register_Error_YourIpIsBanned');
        $error = true;
}
//if there is coincidence, no register allowed for that IP - he already has an account!
if ($already_reg2 >= 1){
        $form_username_error[] = $main_smarty->get_config_vars('Register_Error_YourIpIsBanned');
        $error = true;
}

正如你所看到的，我们检查了最近两天的用户IP。如何使用LOOP在N天前检查用户IP？（N=30天）

如何将"prefix_users"更改为常规模式，而不直接使用"prefix"单词？（用户表）