Merge multiple result tables and perform final query on result - postgresql

Question

I have a function returning table, which accumulates output of multiple calls to another function returning table. I would like to perform final query on built table before returning result. Currently I implemented this as two functions, one accumulating and one performing final query, which is ugly:
CREATE OR REPLACE FUNCTION func_accu(LOCATION_ID INTEGER, SCHEMA_CUSTOMER TEXT)
RETURNS TABLE("networkid" integer, "count" bigint) AS $$
DECLARE
GATEWAY_ID integer;
BEGIN
FOR GATEWAY_ID IN
execute format(
'SELECT id FROM %1$I.gateway WHERE location_id=%2$L'
, SCHEMA_CUSTOMER, LOCATION_ID)
LOOP
RETURN QUERY execute format(
'SELECT * FROM get_available_networks_gw(%1$L, %2$L)'
, GATEWAY_ID, SCHEMA_CUSTOMER);
END LOOP;
END;
$$ LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION func_query(LOCATION_ID INTEGER, SCHEMA_CUSTOMER TEXT)
RETURNS TABLE("networkid" integer, "count" bigint) AS $$
DECLARE
BEGIN
RETURN QUERY execute format('
SELECT networkid, max(count) FROM func_accu(%2$L, %1$L) GROUP BY networkid;'
, SCHEMA_CUSTOMER, LOCATION_ID);
END;
$$ LANGUAGE plpgsql;
How can this be done in single function, elegantly?

Answer 1

Both functions simplified and merged, also supplying value parameters in the USING clause:
CREATE OR REPLACE FUNCTION pg_temp.func_accu(_location_id integer, schema_customer text)
RETURNS TABLE(networkid integer, count bigint) AS
$func$
BEGIN
RETURN QUERY EXECUTE format('
SELECT f.networkid, max(f.ct)
FROM %I.gateway g
, get_available_networks_gw(g.id, $1) f(networkid, ct)
WHERE g.location_id = $2
GROUP BY 1'
, _schema_customer)
USING _schema_customer, _location_id;
END
$func$ LANGUAGE plpgsql;
Call:
SELECT * FROM func_accu(123, 'my_schema');
Related:
Dynamically access column value in record
I am using alias names for the columns returned by the function (f(networkid, ct)) to be sure because you did not disclose the return type of get_available_networks_gw(). You can use the column names of the return type directly.
The comma (,) in the FROM clause is short syntax for CROSS JOIN LATERAL .... Requires Postgres 9.3 or later.
What is the difference between LATERAL and a subquery in PostgreSQL?
Or you could run this query instead of the function:
SELECT f.networkid, max(f.ct)
FROM myschema.gateway g, get_available_networks_gw(g.id, 'my_schema') f(networkid, ct)
WHERE g.location_id = $2
GROUP BY 1;