Oracle 18c

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select * from V$VERSION;


BANNER
BANNER_FULL
BANNER_LEGACY
CON_ID


Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
0


create table tab (id, name, sdt, edt) as
    select 1, 'name1', date'2020-01-15', date'2020-08-06' from dual union all
    select 2, 'name2', date'2020-03-14', date'2020-11-25' from dual union all
    select 3, 'name3', date'2020-08-01', date'2020-10-31' from dual 
3 rows affected

with params as (
    select date'2020-01-01' from#, 12 months# from dual
)
select to_char (mon, 'Mon rr') month, count (id) 
from (
    select add_months (trunc (from#, 'mm'), level-1) mon 
    from params connect by level<=months#)
left join tab t on (t.sdt <= last_day (mon) and t.edt >= mon)   
group by mon
order by mon
/


MONTH
COUNT(ID)


Jan 20
1

Feb 20
1

Mar 20
2

Apr 20
2

May 20
2

Jun 20
2

Jul 20
2

Aug 20
3

Sep 20
2

Oct 20
2

Nov 20
1

Dec 20
0

MONTH	COUNT(ID)
Jan 20	1
Feb 20	1
Mar 20	2
Apr 20	2
May 20	2
Jun 20	2
Jul 20	2
Aug 20	3
Sep 20	2
Oct 20	2
Nov 20	1
Dec 20	0