sql - Drupal 7 多选连接语法

Question

很难让我的头脑围绕多个连接。谁能告诉我为什么这是错误的？

*编辑*

$query = db_select('node', 'n');
$query->join('file_usage', 'fu', 'fu.id = n.nid');
$query->join('field_data_field_featured_image', 'ffimage', 'ffimage.entity_id = n.nid');
$query->join('file_managed', 'fm', 'fm.fid = n.nid');

$query
->fields('fu', array('id'))
->fields('fm', array('filename'))
->fields('ffimage', array('field_featured_image_title'))
->fields('n', array('nid', 'title'))
->condition('n.type', 'work')
->orderby('n.nid', 'DESC')
->range(0, 20);

$result = $query->execute();
foreach ($result as $record) {
echo '<li>';    
echo '<div class="home_text"><h1>'.$record->title.'</h1></div>';
echo '<a href="...some_node/';
echo $record->id;
echo '">';
echo '<img src="...some_files/';
echo $record->filename;
echo '" width="960px" height="615px" />';
echo '</a>';
echo '</li>';   
}