drupal 连表查询+分页

$query = db_select('Table','t');
     $query->join('Table_A','a','on条件);
     $query->join('Table_B','b','on条件'); 

     $objects=$query->extend('PagerDefault')//重要，extend('PagerDefault')实现分页
     ->fields('t', array( 'colname_1','colname_2')) 

     ->fields('b', array( 'colname_1','colname_2')) 

      ->fields('b', array( 'colname_1','colname_2')) 
     ->condition('t.status',1) ->condition('a.status',1) 
     ->orderBy('n.created','DESC') ->limit(1) -> execute() ; 

$output=""; 
$rows = array(); 

$title_length=25; 

foreach ($objects as $key => $object) 
{ 

    $row = array(); 

    $title=""; 

    if (strlen($object -> filename)>$title_length) { 

　　    $title= drupal_substr($object -> filename,0,50).'...' ;//最多显示12个字  
    } 
    else { $title= $object -> filename ;//最多显示12个字  } 
    $url_head='http://'.$_SERVER['HTTP_HOST'].'/drupal755/sites/default/files/'; 

    $url=$url_head.ltrim($object->uri,'public://'); 

    $row['title']=l($object -> filename,$url); 

    $row['created']=date('Y-m-d',$object->created); $rows[] = $row; 
} 

$results=$rows; 

$output .= theme('table', array('rows' => $rows)); 

$output .= theme('pager'); return $output;