Programmatically setting images as thumbnails in Magento

magento-set-images.php

<?php
require_once 'app/Mage.php';
Mage::app();

mysql_connect(localhost, DATABASE_USER, DATABASE_PASSWORD);
mysql_select_db(DATABASE_NAME) or die("Unable to select database");

$result = mysql_query("SELECT * FROM `catalog_product_entity_varchar` WHERE attribute_id in (74,75,76) AND value='no_selection'");

while ($row = mysql_fetch_array($result)) {
    $id = $row["entity_id"];
    $product = Mage::getModel("catalog/product")->load($id);
    $mediaGallery = $product->getMediaGallery();
    if ($mediaGallery["images"][0]["file"] != '' || $mediaGallery["images"][0]["file"] != NULL) {
        $path = $mediaGallery["images"][0]["file"];
        $update_result = mysql_query("UPDATE `catalog_product_entity_varchar` SET VALUE='".$path."' WHERE attribute_id in (74,75,76) and entity_id=".$id);
        echo "set images for product ".$id."<br />";
    }
}
?>