select 'table-A' as bo_table, '테이블A' as bo_subject, wr_id, wr_subject, wr_datetime from tabel-A  

union

select 'table-B' as bo_table, '테이블B' as bo_subject, wr_id, wr_subject, wr_datetime from table-B 

order by wr_datetime desc  

limit 5;