这话怎么理解?: $query = "SELECT a.id,a.dirname FROM dir AS a,dir AS b WHERE b.dirname='{$topicnl_name}' AND a.id=b.parent_id";

$query = "SELECT a.id,a.dirname FROM dir AS a,dir AS b WHERE b.dirname='{$topicnl_name}' AND a.id=b.parent_id"; $query = "SELECT a.id,a.dirname FROM dir AS a,d