Postgres 14

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create table source(id int, external_id int, resolution varchar(10), timestamp2 timestamp);
insert into source values(1,	1	,'1D',	to_timestamp(1645941482));
insert into source values(2,	1	,'1D',	to_timestamp(1645941481));
insert into source values(3,	1	,'1D',	to_timestamp(1645941484));
insert into source values(4,	2	,'1D',	to_timestamp(1645941483));
insert into source values(5,	2	,'1D',	to_timestamp(1645941463));
insert into source values(6,	3	,'1D',	to_timestamp(1645941183));
insert into source values(7,	3	,'1D',	to_timestamp(1645941483));
insert into source values(8,	3	,'1D',	to_timestamp(1646941483));
insert into source values(8,	3	,'1D',	to_timestamp(1645741488));
insert into source values(10,	3	,'1D',	to_timestamp(1645941490));
insert into source values(11,	1	,'3D',	to_timestamp(1645941494));
insert into source values(12,	1	,'3D',	to_timestamp(1645941491));
insert into source values(13,	2	,'3D',	to_timestamp(1645941496));
insert into source values(14,	2	,'3D',	to_timestamp(1645941490));
insert into source values(15,	2	,'3D',	to_timestamp(1645941493));
insert into source values(16,	2	,'3D',	to_timestamp(1645941491));
insert into source values(17,	3	,'3D',	to_timestamp(1645941492));
1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

with cte as
(
  select id,external_id, resolution, row_number()over(partition by external_id,resolution order by timestamp2)rn from source
)
SELECT external_id, resolution, string_agg(id::text, ',') ids
FROM cte
where rn<=2
GROUP BY external_id, resolution 


external_id
resolution
ids


1
1D
2,1

1
3D
12,11

2
1D
5,4

2
3D
14,16

3
1D
8,6

3
3D
17