Lederboards in PostgreSQL and get 2 next and previous rows - postgresql

Question

We use Postgresql 14.1
I have a sample data that contains over 50 million records.
base table:
+------+----------+--------+--------+--------+
| id | item_id | battles| wins | damage |
+------+----------+--------+--------+--------+
| 1 | 255 | 35 | 52.08 | 1245.2 |
| 2 | 255 | 35 | 52.08 | 1245.2 |
| 3 | 255 | 35 | 52.08 | 1245.3 |
| 4 | 255 | 35 | 52.08 | 1245.3 |
| 5 | 255 | 35 | 52.09 | 1245.4 |
| 6 | 255 | 35 | 52.08 | 1245.3 |
| 7 | 255 | 35 | 52.08 | 1245.3 |
| 8 | 255 | 35 | 52.08 | 1245.7 |
| 1 | 460 | 18 | 47.35 | 1010.1 |
| 2 | 460 | 27 | 49.18 | 1518.9 |
| 3 | 460 | 16 | 50.78 | 1171.2 |
+------+----------+--------+--------+--------+
We need to get the target row number and 2 next and 2 previous rows as quickly as possible.
Indexed columns:
id
item_id
Sorting:
damage (DESC)
wins (DESC)
battles (ASC)
id (ASC)
At the example, we need to find the row number and +- 2 rows where id = 4 and item_id = 255. The result table should be:
+------+----------+--------+--------+--------+------+
| id | item_id | battles| wins | damage | rank |
+------+----------+--------+--------+--------+------+
| 5 | 255 | 35 | 52.09 | 1245.4 | 2 |
| 3 | 255 | 35 | 52.08 | 1245.3 | 3 |
| 4 | 255 | 35 | 52.08 | 1245.3 | 4 |
| 6 | 255 | 35 | 52.08 | 1245.3 | 5 |
| 7 | 255 | 35 | 52.08 | 1245.3 | 6 |
+------+----------+--------+--------+--------+------+
How can I do this with Row number windows function?
Is there is any way optimize in query to make it faster because other columns have no indexes?
CREATE OR REPLACE FUNCTION find_top(in_id integer, in_item_id integer) RETURNS TABLE (
r_id int,
r_item_id int,
r_battles int,
r_wins real,
r_damage real,
r_rank bigint,
r_eff real,
r_frags int
) AS $$
DECLARE
center_place bigint;
BEGIN
SELECT place INTO center_place FROM
(SELECT
id, item_id,
ROW_NUMBER() OVER (ORDER BY damage DESC, wins DESC, battles, id) AS place
FROM
public.my_table
WHERE
item_id = in_item_id
AND battles >= 20
) AS s
WHERE s.id = in_id;
RETURN QUERY SELECT
s.place, pt.id, pt.item_id, pt.battles, pt.wins, pt.damage
FROM
(
SELECT * FROM
(SELECT
ROW_NUMBER () OVER (ORDER BY damage DESC, wins DESC, battles, id) AS place,
id, item_id
FROM
public.my_table
WHERE
item_id = in_item_id
AND battles >= 20) x
WHERE x.place BETWEEN (center_place - 2) AND (center_place + 2)
) s
JOIN
public.my_table pt
ON pt.id = s.id AND pt.item_id = s.item_id;
END;
$$ LANGUAGE plpgsql;

Answer 1

CREATE OR REPLACE FUNCTION find_top(in_id integer, in_item_id integer) RETURNS TABLE (
r_id int,
r_item_id int,
r_battles int,
r_wins real,
r_damage real,
r_rank bigint,
r_eff real,
r_frags int
) AS $$
BEGIN
RETURN QUERY
SELECT c.*, B.ord -3 AS row_number
FROM
( SELECT array_agg(id) OVER w AS id
, array_agg(item_id) OVER w AS item_id
FROM public.my_table
WINDOW w AS (ORDER BY damage DESC, wins DESC, battles, id ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
) AS a
CROSS JOIN LATERAL unnest(a.id, a.item_id) WITH ORDINALITY AS b(id, item_id, ord)
INNER JOIN public.my_table AS c
ON c.id = b.id
AND c.item_id = b.item_id
WHERE a.item_id[3] = in_item_id
AND a.id[3] = in_id
ORDER BY b.ord ;
END ; $$ LANGUAGE plpgsql;
test result in dbfiddle