I am wanting to not echo out the comma at the end of the echo after the last row. How can I do that? Here is my code:

<?php
    header("Content-type: application/json");
    echo '{"points":[';

    mysql_connect("localhost", "user", "password");
    mysql_select_db("database");

    $q = "SELECT venues.id, venues.lat, venues.lon, heat_indexes.temperature FROM venues, heat_indexes WHERE venues.id = heat_indexes.venue_id";

    $res = mysql_query($q) or die(mysql_error());
    while ($point = mysql_fetch_assoc($res)) {
    echo $point['lat'] . "," . $point['lon'] . "," . $point['temperature'] . ",";
    }
    mysql_free_result($res);
    echo ']}';
    ?>