Select by active record... help

[eluser]Unknown[/eluser]
Hello!

I'm sorry for my English

I try to select from database (mysql) by ActiveRecord

Code:

$this->db->select('results.id_url, results.checktime, results.result, results.responsetime, results.responselength, results.responsespeed, urls.url')
->from('results,url_urls')
->where(array("url_results.id_url" =>$urlId,"url_urls.id_url"=>"url_results.id_url"))
->get();
echo $this->db->last_query();

sql code of this query:

SELECT `url_results`.`id_url`, `url_results`.`checktime`, `url_results`.`result`, `url_results`.`responsetime`, `url_results`.`responselength`, `url_results`.`responsespeed`, `url_urls`.`url` FROM (`url_results`, `url_urls`) WHERE `url_results`.`id_url` = '1' AND `url_urls`.`id_url` = 'url_results.id_url'

please, Help me to create righty query I don't know how make condition part

If I write '...->where("url_results.id_url =".$urlId." and url_urls.id_url = url_results.id_url")' to query return data, but this syntax does not suit me...

UPD: I'm using tableprefix "url_"