How to select unique records in PostgreSQL

Hi All,

I want to get the unique wallet_id from this table even it was repeated on
multiple occasions I should calculate only once as well as if the wallet_id
was calculated on previous month it shouldn't be calculate on next months

create table student_id
(
student_wallet_id int,
card_id int,
created_date date
)

insert into student_id values ('w1', 'c1', '2022-04-01')

insert into student_id values ('w1', 'c2', '2022-04-03')

insert into student_id values ('w1', 'c3', '2022-04-04')

insert into student_id values ('w1', 'c4', '2022-05-01')
insert into student_id values ('w2', 'c1', '2022-05-01')
insert into student_id values ('w2', 'c2', '2022-05-04')
insert into student_id values ('w3', 'c4', '2022-05-05')
insert into student_id values ('w3', 'c6', '2022-06-03)
insert into student_id values ('w3', 'c7', '2022-06-05')
insert into student_id values ('w3', 'c8', '2022-06-07')
expected output:
-------------------

months count_wallet_id
2022-04 1
2022-05 2
2022-05 0

Regards

A.Rama Krishnan