Temporary tables are often used to store transient data in batch processing and the contents can be accessed multiple times. However, frequent use of temporary tables has a problem that the system catalog tends to bloat. I know there has been several proposals to attack this problem, but I would like to propose a new one.
The idea is to use Ephemeral Named Relation (ENR) like a temporary table. ENR information is not stored into the system catalog, but in QueryEnvironment, so it never bloat the system catalog.
Although we cannot perform insert, update or delete on ENR, I wonder it could be beneficial if we need to reference to a result of a query multiple times in a batch processing.
The attached is a concept patch. This adds a new syntax "OPEN cursor INTO TABLE tablename" to pl/pgSQL, that stores a result of the cursor query into a ENR with specified name. However, this is a tentative interface to demonstrate the concept of feature.
Here is an example;
postgres=# \sf fnc CREATE OR REPLACE FUNCTION public.fnc() RETURNS TABLE(sum1 integer, avg1 integer, sum2 integer, avg2 integer) LANGUAGE plpgsql AS $function$ DECLARE sum1 integer; sum2 integer; avg1 integer; avg2 integer; curs CURSOR FOR SELECT aid, bid, abalance FROM pgbench_accounts WHERE abalance BETWEEN 100 AND 200; BEGIN OPEN curs INTO TABLE tmp_accounts; SELECT count(abalance) , avg(abalance) INTO sum1, avg1 FROM tmp_accounts; SELECT count(bbalance), avg(bbalance) INTO sum2, avg2 FROM tmp_accounts a, pgbench_branches b WHERE a.bid = b.bid; RETURN QUERY SELECT sum1,avg1,sum2,avg2; END; $function$
As above, we can use the same query result for multiple aggregations, and also join it with other tables.
What do you think of using ENR for this way?
The idea looks pretty good. I think it can be very useful. I am not sure if this design is intuitive. If I remember well, the Oracle's has similar features, and can be nice if we use the same or more similar syntax (although I am not sure how it can be implementable)? I think so PL/SQL design has an advantage, because you don't need to solve the scope of the cursor's assigned table.
OPEN curs INTO TABLE tmp_accounts; -- it looks little bit strange. I miss info, so tmp_accounts is not normal table
