cnk.sql

with c(id) as (select get_combinations((select array_agg(id order by id) from test), 4))
select id
from c
where array[1,2,3,4] = (select array_agg(i order by i) from test where array[id] <@ c.id);

create or replace function get_combinations(source anyarray, size int) returns setof anyarray as $$
 with recursive combinations(combination, indices) as (
   select source[i:i], array[i] from generate_subscripts(source, 1) i
   union all
   select c.combination || source[j], c.indices || j
   from   combinations c, generate_subscripts(source, 1) j
   where  j > all(c.indices) and
          array_length(c.combination, 1) < size
 )
 select combination from combinations
 where  array_length(combination, 1) = size;
$$ language sql;