Postgres 10

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CREATE TABLE test(
   id         INTEGER  NOT NULL 
  ,account_id INTEGER  NOT NULL
  ,sha256     VARCHAR(40) NOT NULL
  ,size       INTEGER  NOT NULL
);
INSERT INTO test
(id,account_id,sha256,size) VALUES 
(1,1,'abc',120),
(2,1,'abc',120),
(3,1,'bcd',150),
(4,2,'abc',120),
(5,2,'def',80),
(6,3,'fed',100),
(7,3,'fed',100);
7 rows affected

select   *  from (
select id,account_id,sha256,size,
ROW_NUMBER () OVER (
		PARTITION BY  account_id,sha256,size
		ORDER BY
			id asc
			)  rn 
			
from test) f
where rn=1


id
account_id
sha256
size
rn


1
1
abc
120
1

3
1
bcd
150
1

4
2
abc
120
1

5
2
def
80
1

6
3
fed
100
1


select  SUM(f.size) AS total from (
select id,account_id,sha256,size,
ROW_NUMBER () OVER (
		PARTITION BY  account_id,sha256,size
		ORDER BY
			id asc
			)  rn 
			
from test) f
where rn=1


total


570