select m.user_name, b.user_id, substring_index( date,'-', 3) as mon ,count(*) as cnt from board_write_sale b left join xe_member m on m.user_id=b.user_id where b.date!='' and b.board_id='meet' and b.host_name!='' group by substring_index( date,'-', 3)
1055 : Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'pjh814028.m.user_name' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
error file : /busi/meeting_list.php