<?php
if (isset($_POST['submit'], $_POST['username'])) {
// sanitize your $_POST values
$count = count($_POST['groupname']);
    for ($i = 0; $i < $count; $i++) {
        $username = $_POST['username'];
        $groupname = $_POST['groupname'][$i];
        $rate = $_POST['rate'][$i];
        $sql = "INSERT INTO reseller_table (username, groupname, rate) VALUES ('{$username}','{$groupname}','{$rate}')";
    }
}