Create temp table in a STABLE stored procedure in postgresql - postgresql

Question

I would like to create a temp table in a stored procedure which has a STABLE volatility category setted to store the result of a select for later usage in the stored procedure. At the end of the stored procedure this temp table is deallocated and i am sure that this temp table does not have any affect on the database, because as far as i know with this volatility category i ensure the optimizer that this stored procedure will not affect the database.
So i would like to do something like this:
Create a stored procedure which returns with a query:
CREATE OR REPLACE FUNCTION storedproc()
RETURNS TABLE
(Egy TEXT,
Ketto TEXT)
AS $$
BEGIN
RETURN QUERY SELECT * FROM temptable;
END;
$$ LANGUAGE plpgsql;
Create a stored procedure which is using the previous query:
CREATE OR REPLACE FUNCTION stablefunction()
RETURNS TABLE
(Egy TEXT,
Ketto TEXT)
AS $$
BEGIN
-- I would like to store the results here for later usage
CREATE TEMP TABLE buba AS select * from storedproc();
-- Do other stuff
-- ...
-- Reuse the results here which was stored before
END;
$$ LANGUAGE plpgsql
STABLE;
But when i want to execute this stored procedure as this:
DO
$$
BEGIN
perform stablefunction() ;
END;
$$ LANGUAGE plpgsql;
i get the following error message:
ERROR: CREATE TABLE AS is not allowed in a non-volatile function
Maybe this is not the intended usage of the stored procedures, but then is there a way for store the result of a query inside of the stored procedure for later usage in the same stored procedure, maybe like a handle or somethings?

Answer 1

The documentation states clearly: A stable function cannot modify the database. A temporary table is a part of a database as well, so you cannot create it, insert into, delete from etc. Your concept seems a bit strange but I don't want to judge it. There is a trick that allows what you want to do. Perfom all actions on the temp table using other functions that do not have to be stable. Example:
create or replace function create_my_temp_table()
returns void language plpgsql volatile as $$
begin
create temp table temp_table(id int);
insert into temp_table values (123);
end $$;
create or replace function stable_function()
returns text language plpgsql stable as $$
begin
perform create_my_temp_table();
return 'ok';
end $$;
Test:
select stable_function();
stable_function
-------------
ok
(1 row)
select * from temp_table;
id
-----
123
(1 row)