참고하세요

with tbl as (

     select 'A' nm,  '01월' dt union all

     select 'A' nm,  '02월' dt union all

     select 'B' nm,  '01월' dt union all

     select 'B' nm,  '02월' dt union all

     select 'B' nm,  '02월' dt union all

     select 'B' nm,  '04월' dt union all

     select 'C' nm,  '05월' dt

),

     mon as (

     select '01월' dt union all

     select '02월' dt union all

     select '03월' dt union all

     select '04월' dt union all

     select '05월' dt union all

     select '06월' dt union all

     select '07월' dt union all

     select '08월' dt union all

     select '09월' dt union all

     select '10월' dt union all

     select '11월' dt union all

     select '12월' dt

)

select mon.dt

     , count(case when nm = 'A' then 1 end) nm_A

     , count(case when nm = 'B' then 1 end) nm_B

     , count(case when nm = 'C' then 1 end) nm_C

     , count(case when nm = 'D' then 1 end) nm_D

  from mon 

  left outer join tbl

    on tbl.dt = mon.dt  

 group by mon.dt