select 月份,seller_name from (  select '2019M5' as '月份', seller_name,sum(gmv) as sum   from purchase   where datepart(m,dt)=5   group by seller_name   order by sum   limit 50)   union select 月份,seller_name from (  select '2019M6' as '月份', seller_name,sum(gmv) as sum   from purchase   where datepart(m,dt)=6  group by seller_name   order by sum   limit 50)  ; 不晓得对不对