Looping SQL query - PostgreSQL - postgresql

Question

I'm trying to get a query to loop through a set of pre-defined integers:
I've made the query very simple for this question.. This is pseudo code as well obviously!
my_id = 0
WHILE my_id < 10
SELECT * from table where id = :my_id`
my_id += 1
END
I know that for this query I could just do something like where id < 10.. But the actual query I'm performing is about 60 lines long, with quite a few window statements all referring to the variable in question.
It works, and gets me the results I want when I have the variable set to a single figure.. I just need to be able to re-run the query 10 times with different variables hopefully ending up with one single set of results.
So far I have this:
CREATE OR REPLACE FUNCTION stay_prices ( a_product_id int ) RETURNS TABLE (
pid int,
pp_price int
) AS $$
DECLARE
nights int;
nights_arr INT[] := ARRAY[1,2,3,4];
j int;
BEGIN
j := 1;
FOREACH nights IN ARRAY nights_arr LOOP
-- query here..
END LOOP;
RETURN;
END;
$$ LANGUAGE plpgsql;
But I'm getting this back:
ERROR: query has no destination for result data
HINT: If you want to discard the results of a SELECT, use PERFORM instead.
So do I need to get my query to SELECT ... INTO the returning table somehow? Or is there something else I can do?
EDIT: this is an example of the actual query I'm running:
\x auto
\set nights 7
WITH x AS (
SELECT
product_id, night,
LAG(night, (:nights - 1)) OVER (
PARTITION BY product_id
ORDER BY night
) AS night_start,
SUM(price_pp_gbp) OVER (
PARTITION BY product_id
ORDER BY night
ROWS BETWEEN (:nights - 1) PRECEDING
AND CURRENT ROW
) AS pp_price,
MIN(spaces_available) OVER (
PARTITION BY product_id
ORDER BY night
ROWS BETWEEN (:nights - 1) PRECEDING
AND CURRENT ROW
) AS min_spaces_available,
MIN(period_date_from) OVER (
PARTITION BY product_id
ORDER BY night
ROWS BETWEEN (:nights - 1) PRECEDING
AND CURRENT ROW
) AS min_period_date_from,
MAX(period_date_to) OVER (
PARTITION BY product_id
ORDER BY night
ROWS BETWEEN (:nights - 1) PRECEDING
AND CURRENT ROW
) AS max_period_date_to
FROM products_nightlypriceperiod pnpp
WHERE
spaces_available >= 1
AND min_group_size <= 1
AND night >= '2016-01-01'::date
AND night <= '2017-01-01'::date
)
SELECT
product_id as pid,
CASE WHEN x.pp_price > 0 THEN x.pp_price::int ELSE null END as pp_price,
night_start as from_date,
night as to_date,
(night-night_start)+1 as duration,
min_spaces_available as spaces
FROM x
WHERE
night_start = night - (:nights - 1)
AND min_period_date_from = night_start
AND max_period_date_to = night;
That will get me all the nights night periods available for all my products in 2016 along with the price for the period and the max number of spaces I could fill in that period.
I'd like to be able to run this query to get all the periods available between 2 and 30 days for all my products.
This is likely to produce a table with millions of rows. The plan is to re-create this table periodically to enable a very quick look up of what's available for a particular date. The products_nightlypriceperiod represents a night of availability of a product - e.g. Product X has 3 spaces left for Jan 1st 2016, and costs £100 for the night.

Answer 1

Why use a loop? You can do something like this (using your first query):
with params as (
select generate_series(1, 10) as id
)
select t.*
from params cross join
table t
where t.id = params.id;
You can modify params to have the values you really want. Then just use cross join and let the database "do the looping."