Postgres 12

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CREATE TABLE mytable(
   user_id  INTEGER  NOT NULL
  ,amount   INTEGER  NOT NULL
  ,trandate DATE   NOT NULL
);
INSERT INTO mytable(user_id,amount,trandate) VALUES (1,12,'2020-09-12');
INSERT INTO mytable(user_id,amount,trandate) VALUES (1,4,'2020-10-02');
INSERT INTO mytable(user_id,amount,trandate) VALUES (1,8,'2020-11-12');
INSERT INTO mytable(user_id,amount,trandate) VALUES (2,23,'2020-12-02');
INSERT INTO mytable(user_id,amount,trandate) VALUES (2,45,'2021-01-12');
INSERT INTO mytable(user_id,amount,trandate) VALUES (2,7,'2021-02-02');
1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

select distinct on (user_id) t.*
from mytable t
order by user_id, amount;


user_id
amount
trandate


1
4
2020-10-02

2
7
2021-02-02


select user_id, min(amount)
from mytable t
group by user_id;


user_id
min


2
7

1
4


select
user_id, amount, trandate
from (
    select user_id, amount, trandate
        , row_number() over(partition by user_id order by amount) as rn
    from mytable
    ) t
where rn = 1
    


user_id
amount
trandate


1
4
2020-10-02

2
7
2021-02-02