Oracle 18c

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
create table table_a (id, VLD_FRM_TMS) as
select 42, timestamp '2021-02-28 00:00:00.0' from dual;
1 rows affected

create table table_b (id, strt_dt) as
select 42, date '2020-10-29' from dual;
1 rows affected

select a.ID, floor (months_between (cast(a.VLD_FRM_TMS as date), STRT_DT)) as delta
from TABLE_A a
inner join TABLE_B b
on a.ID = b.ID


ID
DELTA


42
3


select a.ID,
  cast(a.VLD_FRM_TMS as date),
  STRT_DT,
  months_between (cast(a.VLD_FRM_TMS as date), STRT_DT),
  floor (months_between (cast(a.VLD_FRM_TMS as date), STRT_DT)) as delta
from TABLE_A a
inner join TABLE_B b
on a.ID = b.ID


ID
CAST(A.VLD_FRM_TMSASDATE)
STRT_DT
MONTHS_BETWEEN(CAST(A.VLD_FRM_TMSASDATE),STRT_DT)
DELTA


42
28-FEB-21
29-OCT-20
3.96774193548387096774193548387096774194
3


select a.ID,
  trunc(a.VLD_FRM_TMS, 'MM'),
  trunc(STRT_DT, 'MM'),
  months_between (trunc(a.VLD_FRM_TMS, 'MM'), trunc(STRT_DT, 'MM')) as delta
from TABLE_A a
inner join TABLE_B b
on a.ID = b.ID


ID
TRUNC(A.VLD_FRM_TMS,'MM')
TRUNC(STRT_DT,'MM')
DELTA


42
01-FEB-21
01-OCT-20
4