possible to have multiple temp tables per postgres function? - postgresql

Question

i'm trying to find the total number of contacts who ARE in some lists, but who are NOT in others. basically i want to get the set difference between these two groups of contacts.
here's my function. i'm using supabase. this function works perfectly via the supabase browser sql editor
CREATE or replace FUNCTION get_net_num_contacts(to_list_ids bigint[], not_to_list_ids bigint[])
returns bigint
AS $$
declare
net_num_contacts bigint;
BEGIN
CREATE TEMP TABLE IF NOT EXISTS t1 AS
select distinct list_members.contact_id from list_members where list_members.list_id = ANY(to_list_ids);
CREATE TEMP TABLE IF NOT EXISTS t2 AS
select distinct list_members.contact_id from list_members where list_members.list_id = ANY(not_to_list_ids);
CREATE TEMP TABLE IF NOT EXISTS t3 AS
select t1.contact_id from t1 except select t2.contact_id from t2;
SELECT count(*) from t3 into net_num_contacts;
return net_num_contacts;
END;
$$ LANGUAGE plpgsql;
but when i save this to my db and try running it in my web app with an .rpc call, it always returns 0.
i did some tinkering and found that the function, loaded into supabase via my filesystem (supabase start), started returning empty sets any time i tried to create 2 or more temp tables.
this works great:
CREATE or replace FUNCTION demo_works(to_list_ids bigint[], not_to_list_ids bigint[])
returns setof bigint
AS $$
declare
net_num_contacts bigint;
BEGIN
CREATE TEMP TABLE IF NOT EXISTS t1 AS
select distinct list_members.contact_id from list_members where list_members.list_id = ANY(to_list_ids);
return query select * from t1;
END;
$$ LANGUAGE plpgsql;
doesn't work, always returns an empty array:
CREATE or replace FUNCTION demo_doesnt_work(to_list_ids bigint[], not_to_list_ids bigint[])
returns setof bigint
AS $$
declare
net_num_contacts bigint;
BEGIN
CREATE TEMP TABLE IF NOT EXISTS t1 AS
select distinct list_members.contact_id from list_members where list_members.list_id = ANY(to_list_ids);
CREATE TEMP TABLE IF NOT EXISTS t2 AS
select distinct list_members.contact_id from list_members where list_members.list_id = ANY(not_to_list_ids);
return query select * from t1;
END;
$$ LANGUAGE plpgsql;
i've seen hints online that maybe it's understood that you can't have multiple temp tables in postgres (i lost the link), and indications that some systems dont allow temp tables in functions at all.
so i'm confused as to why this works in the supabase sql editor but not after being saved into my db. and hoping to gain clarity on the limitations here, or maybe i'm doing something irrelevant wrong.
and if anyone has insight on how to properly accomplish what i'm trying to do, that would be great too
update
here's my successful alternative function for getting the set difference between these two groups of contacts, if useful for anyone. and open to feedback. but i'm still very curious about why my initial attempt didn't usually work.
CREATE or replace FUNCTION get_net_num_contacts(to_list_ids bigint[], not_to_list_ids bigint[])
returns bigint
AS $$
declare
net_num_contacts bigint;
BEGIN
WITH r0 as
(
WITH r1 AS
(
select distinct contact_id from list_members where list_id = ANY(to_list_ids)
)
select contact_id from r1 except
select contact_id from list_members where list_id = ANY(not_to_list_ids)
)
select count(*) from r0 into net_num_contacts;
return net_num_contacts;
END;
$$ LANGUAGE plpgsql;