Сократить запрос к БД

<?php
    // FUNCTION get Price Group
    function getPricegroup($country_name){
    global $mysqli;
    connectDB();
    $result_set=$mysqli->query("SELECT `price_group` FROM `country` WHERE `country_name`='$country_name'");
    $row=$result_set->fetch_assoc();
    closeDB();
    return $row['price_group'];
    }
    // FUNCTION EMS COST
    function getCostEms($price_group,$weight){
    global $mysqli;
    connectDB();
    $result_set=$mysqli->query("SELECT `cost` FROM `ems_rates` WHERE `price_group`='$price_group' AND `weight`='$weight'");
    $row=$result_set->fetch_assoc();
    closeDB();
    return $row['cost'];
    }
    // FUNCTION PRIORITY COST
    function getCostPriority($price_group,$weight){
    global $mysqli;
    connectDB();
    $result_set=$mysqli->query("SELECT `cost` FROM `prt_rates` WHERE `price_group`='$price_group' AND `weight`='$weight'");
    $row=$result_set->fetch_assoc();
    closeDB();
    return $row['cost'];
    }
    // FUNCTION TNT COST
    function getCostTnt($weight){
    global $mysqli;
    connectDB();
    $result_set=$mysqli->query("SELECT `cost` FROM `tnt_rates` WHERE `weight`='$weight'");
    $row=$result_set->fetch_assoc();
    closeDB();
    return $row['cost'];
    }
?>