Unknown column 'username' in 'field list'SELECT a.id AS id,b.name AS class_name,b.id AS class_id,a.name AS name,a.rank2_id,licence_type,price,a.click_count AS click_count,start_time,content_info AS info,username FROM writing AS a JOIN users ON a.user_id=users.id LEFT JOIN ( SELECT id,name FROM writing_class_b WHERE is_delete=0 AND rank=3 AND rank2 = 17 ) AS b ON a.rank3_id=b.id WHERE a.is_delete=0 AND verifing<>'down' AND rank2_id=17 ORDER by a.id DESC LIMIT 0 , 20