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How to select unique records in PostgreSQL - Mailing list pgsql-general

From Rama Krishnan
Subject How to select unique records in PostgreSQL
Date
Msg-id CAJWX+ENP=04KZ-bHrNpwkqZL0iFuMkDdXnKK4cs0kZNJVnpM4w@mail.gmail.com
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Responses Re: How to select unique records in PostgreSQL
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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

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