Oracle 18c

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create table my_date (my_date date);
insert into my_date values(to_date('11-05-2019','dd-mm-yyyy'))
1 rows affected

alter session set NLS_DATE_FORMAT = 'dd-mon-yyyy'
select * from my_date

MY_DATE

11-may-2019

alter session set NLS_DATE_FORMAT = 'mon-dd-yyyy'
select * from my_date

MY_DATE

may-11-2019

select to_char(my_date,'ddmonyyyy') from my_date;

TO_CHAR(MY_DATE,'DDMONYYYY')

11may2019

select to_char(my_date,'ddyyyy-mm') from my_date;

TO_CHAR(MY_DATE,'DDYYYY-MM')

112019-05