Oracle 18c

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create table as_months (month_name varchar2(30));
insert into as_months select trim(to_char(add_months(sysdate,rownum-1),'MONTH')) from dual connect by rownum <=12
12 rows affected

select * from as_months;

MONTH_NAME

JULY

AUGUST

SEPTEMBER

OCTOBER

NOVEMBER

DECEMBER

JANUARY

FEBRUARY

MARCH

APRIL

MAY

JUNE

select to_char(sysdate, 'MM') from dual;

TO_CHAR(SYSDATE,'MM')

07

select * from as_months
WHERE CASE WHEN to_char(sysdate, 'MM') in ('01','02','03') THEN case when month_name in ('OCTOBER','NOVEMBER','DECEMBER') then 1 else 0 end
           WHEN to_char(sysdate, 'MM') in ('04','05','06') THEN case when month_name in('JANUARY','FEBRUARY','MARCH')  then 1 else 0 end
           WHEN to_char(sysdate, 'MM') in ('07','08','09') THEN case when month_name in('APRIL','MAY','JUNE') then 1 else 0 end
           WHEN to_char(sysdate, 'MM') in ('10','11','12') THEN case when month_name in('JULY', 'AUGUST', 'SEPTEMBER')  then 1 else 0 end
      END = 1

MONTH_NAME

APRIL

MAY

JUNE