MySQL Query Error, sql: SELECT iid,mid,subject,product,content,hydm,date_format(tm,'%Y/%m/%d') as tm,type,icompany,pic_path,province,city FROM info where flag=1 and hydm='yi16' ORDER BY `tm` DESC LIMIT -20 , 20, ErrMsg: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '-20 , 20' at line 1