with patient(keyid, "NUMBER", fam, im, ot, dat_rozhd) as (select 1, 4444, 'Иванов','Иван','Иванович',date'1990-01-01'
from dual union all select 2, 4446, 'Иванов','Петр','Иванович',date'1989-01-01'
from dual union all select 4, 4447, 'Петров','Иван','Иванович',date'1980-01-01'
from dual union all select 5, 4448, 'Михайлов','Иван','Сергеевич',date'1945-01-01'
from dual union all select 6, 4478, 'Гусев','Иван','Сергеевич',date'1985-01-01'
from dual union all select 8, 4480, 'Михайлов','Иван','Сергеевич',date'1945-01-01'
from dual)
, police (keyid, seriya, nomer, patientid) as (select 1, 'СЕР', '55555', 1
from dual union all select 2, 'СЕР', '55555', 2
from dual union all select 3, 'СЕР', '55555', 5
from dual union all select 4, 'СЕР2', '55345', 4
from dual union all select 5, '', '55555000', 6
from dual union all select 6, '', '55555000', 5
from dual union all select 7, '', '55555000', 8
from dual)
, posechenie(keyid, date_pos /*(дата посещения)*/, patientid) as (select 1, date'2019-01-01', 1
from dual union all select 2, date'2019-01-02', 1
from dual union all select 3, date'2019-01-03', 2
from dual union all select 4, date'2019-01-04', 5
from dual union all select 5, date'2019-01-05', 4
from dual union all select 6, date'2019-01-06', 6
from dual union all select 7, date'2019-01-07', 7
from dual union all select 8, date'2019-01-08', 8
from dual)
---------------------< Сut here >----------------------------
select keyid, fam, im, ot, "NUMBER", seriya, nomer, dat_rozhd
  from (
    select patient.keyid, patient.fam, patient.im, patient.ot, patient."NUMBER"
         , police.seriya, police.nomer, patient.dat_rozhd
         , count(distinct police.patientid) over(partition by police.seriya, police.nomer) f
      from police, patient, posechenie
    where police.patientid=patient.keyid
      and posechenie.patientid=patient.keyid
      and posechenie.date_pos between date'2019-01-01' and date'2019-01-31'
       ) where f > 1
;