带多表选择的空白页

有了这些查询,但在运行时它给了我空白页。也许因为$query->result函数不适合“him”?(这是表达引擎)

$query = $DB->query("SELECT fr.uri AS smth, ch.uri 
                       FROM exp_static_page_caching_uris AS fr,              
                            exp_static_page_caching_queue AS ch 
                      WHERE fr.uri != ch.uri");         

foreach($query->result as $row) {      
  $DB->query($DB->insert_string('exp_static_page_caching_queue',
                                 array('site_id'   => '1',
                                'uri'              => $row['smth']),
                                TRUE));
}