Zend_Db_Table->Join() 指定欄位別名

如果table A和table B要join一塊，但兩者有共同名稱的欄位時你會下以下SQL:

select a.name b.name from member as a join forum as b on a.id = b.memberId where ...

那如果是用Zend_DB_Table要如何寫呢?

$sql = $adapter->select()
               ->from(array('a' => 'member'), 'a.name')
               ->join(array('b' => 'forum'), 'b.memberId = a.id', array('b.name as bName'))
               ->where('xxx = ?', $var)
               ->order('col desc')
               ->query()
               ->fetchAll()