$query = array(
    'SELECT' => 'a.sky, a.url, b.entity',
        'FROM' => 'first AS a',
        'JOIN' => array(
            'INNER JOIN' => 'two AS b',
            'ON' => 'a.sku = b.sky',
            )
        )

$result = $forum_db->query_build($query) or error(__FILE__, __LINE__);

while($screen = $forum_db->fetch_assoc($result)){
$query = array(
    'UPDATE' => 'three'
    'SET' => 'value ='.$screen['url'],
    'WHERE' => 'att=123 AND entt='$screen['entity']

    )
$results = $forum_db->query_build($query) or error(__FILE__, __LINE__);
}