select m.user_name, b.user_id, substring_index( date,'-', 2) as mon ,count(*) as cnt from board_write_sale b left join xe_member m on m.user_id=b.user_id where b.board_id='month' and b.host_name!='' group by b.user_id, substring_index( date,'-', 2) order by b.date desc limit 0, 20
1055 : Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column 'pjh814028.b.date' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
error file : /busi/month_list.php