I need to joinLeft within Zend_Db ala:
$select->joinLeft(array('ATAG' => 'ad_tags'),
array('ADM.id = ATAG.ad_id AND ADM.site_id = ATAG.site_id AND ATAG.tag_id = ?', $input_vars['tag']),
array('tag_id'))
->order('ATAG.tag_id DESC')
->limit('1');
However, I can't use an array as the second parameter, because it only tags a string; how can I pass in the value, without actually embedding it in the string?