conn.query('select s.student_id AS student_id, s.student_name AS student_name from lecture_students l JOIN student s USING (student_id);',function(err,rows){
conn.query('select s.student_id AS student_id, s.student_name AS student_name from lecture_students l JOIN student s USING (student_id) where l.lecture_id=?;',[lecture_id],function(err,rows){