arrays.sql

create table tst_array(
	id int primary key generated always as identity,
	ts int not null,
	value int[] not null
);

insert into tst_array (ts, value)
select
	(i / 20)::int,
	array(
		select distinct (random()*(i % 10 + 1))::int
		from generate_series(1, (random()*(i % 5) + 2)::int)
	)
from generate_series(1, 1000) g (i);

create or replace function set_union(st anyarray, v anyarray) returns anyarray as $$
select array_agg(distinct x)
from unnest(st || v) u (x)
$$ language sql immutable;

create or replace function set_diff(st1 anyarray, st2 anyarray) returns anyarray as $$
select array(
		select v
		from unnest(st1) u (v)
		except
		select v
		from unnest(st2) u (v)
)
$$ language sql immutable;

create aggregate set_union_agg(anyarray) (
	sfunc = set_union,
	stype = anyarray,
	initcond = '{}'
);

select id, ts, value, agg, set_diff(agg, lag(agg) over (partition by ts order by id))
from (
	select id, ts, value, set_union_agg(value) over (partition by a.ts order by a.id) agg
	from tst_array a
	order by a.id, a.ts
) sub;