mysql خطا [1054] : EXECUTE

URI: index.php?option=com_sitemap&Itemid=2473
Message: Unknown column 'u.name' in 'order clause'
SELECT a.id, a.title, a.modified, a.created, a.seotitle, c.seotitle AS seocat, s.seotitle AS seosec FROM elx_content a INNER JOIN elx_sections s ON s.id=a.sectionid INNER JOIN elx_categories c ON c.id=a.catid WHERE a.catid='28' AND a.state='1' AND ( a.publish_up = '1979-12-19 00:00:00' OR a.publish_up <= '2018-06-19 05:23:40' ) AND ( a.publish_down = '2060-01-01 00:00:00' OR a.publish_down >= '2018-06-19 05:23:40' ) AND a.access IN (29) AND ((a.language IS NULL) OR (a.language LIKE '%persian%')) ORDER BY a.created_by_alias, u.name