PSQL replacement for stored procedure, too slow - sql

Question

I have property, each property has contracts, each contract has integer field rental_area.
Previously I had to get the rental_area of all contracts summed by property and this worked.
SELECT
Sum(cr.rental_area) total_property_rental_area,
-- bunch of other cr fields
FROM appdata.contract_rental cr
INNER JOIN appdata.domain_building b1
ON ( b1.building_id = cr.building_id )
INNER JOIN appdata.domain_immovable im1
ON ( im1.immovable_id = b1.immovable_id )
GROUP BY im1.property_id
Now the logic changed, and contract has a list of periods, and one of those periods contain the rental_area of that contract. And finding that correct period needed some special logic.
I tried to join the logic to the query, but could not find a place, where to put it so I had to create stored procedure.
SELECT Sum(p.rental_area) total_property_rental_area
-- bunch of other cr fields
FROM appdata.contract_rental cr
JOIN appdata.rental_period p
ON p.id = Get_current_period_id(cr.contract_rental_id,
cr.end_date_actual)
INNER JOIN appdata.domain_building b1
ON ( b1.building_id = cr.building_id )
INNER JOIN appdata.domain_immovable im1
ON ( im1.immovable_id = b1.immovable_id )
GROUP BY im1.property_id
Procedure:
CREATE OR REPLACE FUNCTION appdata.get_current_period_id(in contract_id_in bigint, in end_date_actual_in Date)
RETURNS bigint AS
$BODY$
DECLARE
period_id bigint;
BEGIN
-- find the period that matches with end date or current date
select id into period_id
from rental_period
where contract_id = contract_id_in
and Coalesce(end_date_actual_in, Now()) >= start_date
order by start_date desc limit 1;
-- if there was no period, just take the first one
IF period_id is null THEN
select id into period_id
from rental_period
where contract_id = contract_id_in
order by start_date asc
limit 1;
END IF;
return period_id;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
But now it is too slow, is there a way to put the period finding logic into the sql to make it faster, without using stored procedure? The point is that, for reach contract, it has to only get single period based on the logic.

Answer 1

Roll out your stored procedure back into the main SQL, the primary hint being coalescing your 2 queries (if one is null then use the other)
Example: Instead of
p.id = Get_current_period_id(cr.contract_rental_id,
cr.end_date_actual)
Use:
p.pid = coalesce(
(select rpx.id
from rental_period rpx
where contract_id = cr.contract_rental_id
and Coalesce(cr.end_date, Now()) >= start_date
order by start_date desc limit 1;
),
( select rpy.id
from rental_period rpy
where contract_id = cr.contract_rental_id
order by start_date asc
limit 1;
)
)
As per the comment below, the following index may also help:
create index on rental_period (contract_id, start_date asc)
be sure to analyze the table afterward to update the statistics.