Issue with array_agg method when aggregating arrays of different lengths - sql

Question

Here is a lateral query which is part of a bigger query:
lateral (
select
array_agg(
sh.dogsfilters
) filter (
where
sh.dogsfilters is not null
) as dependencyOfFoods
from
shelter sh
where
sh.shelterid = ${shelterid}
) filtersOfAnimals,
the problem is with array_agg method as it fails when it has arrays with different lengths like this ("[[7, 9], [7, 9, 8], [8]]")!
The problem is easy to solve using json_agg but later in the query there's a any check like this:
...
where
cd.dogsid = any(filtersOfAnimals.dependencyOfFoods)
and
...
...
But as any will not work on json data which is prepared using json_agg so I can't use it instead of array_agg!
What might be a better solution to this?

Answer 1

Unnest the arrays and re-aggregate:
lateral
(select array_agg(dogfilter) filter (where dogfilter is not null) as dependencyOfFoods
from shelter sh cross join
unnest(sh.dogsfilters) dogfilter
where sh.shelterid = ${shelterid}
) filtersOfAnimals,
It is interesting that Postgres doesn't have a function that does this. BigQuery offers array_concat_agg() which does exactly what you want.

Answer 2

It is ugly, but it works:
regexp_split_to_array(
array_to_string(
array_agg(
array_to_string(value,',')
),','
),',')::integer[]
I don't know if this could be a valid solution from the the performance point of view ...

Answer 3

In PostgreSQL, you can define your own aggregates. I think that this one does what you want:
create function array_concat_agg_tran(anyarray,anyarray) returns anyarray language sql
as $$ select $1||$2 $$;
create aggregate array_concat_agg(anyarray) (sfunc=array_concat_agg_tran, stype=anyarray);
Then:
select array_concat_agg(x) from (values (ARRAY[1,2]),(ARRAY[3,4,5])) f(x);
array_concat_agg
------------------
{1,2,3,4,5}
With a bit more work, you could make it parallelizable as well.