/**
* Returns result of a count(*) query on the given AQL
* using sql_count select type
* @param mixed $aql string | aql array
* @param array $clause
* @return int
*/
public static function count($aql, $clause = array())
{
$rs = aql::sql_result(self::sql($aql, $clause), array('select_type' => 'sql_count'));
return $rs[0]['count'];
}