Get min / max grouped by two columns - mysql

Question

I have 2 tables
Parts table:
id | part_id | group_id
1 | | 1
2 | 1 | 1
3 | | 1
4 | | 2
Each part related to group and can be related to another part (analog)
Offers table:
offer_id | part_id | quantity
1 | 1 | 1
2 | 2 | 2
3 | 2 | 3
4 | 3 | 4
5 | 4 | 5
Each offer related to part
I need to get best offers grouped by part or its related part ordered by lowest / highest quantity.
For group_id 1, when ordered ASC result should be
offer_id | part_id | quantity
1 | 1 | 1
4 | 3 | 4
When ordered DESC result should be
offer_id | part_id | quantity
4 | 3 | 4
3 | 2 | 3
I tried this query
SELECT
pi.offer_id,
pi.part_id,
( SELECT pps.quantity
FROM offers AS pps
WHERE pps.offer_id = pi.offer_id
ORDER BY pps.quantity asc
LIMIT 1
) AS q
FROM offers AS pi
JOIN parts p ON p.id = pi.part_id
WHERE p.group_id = 1
GROUP BY part_id
ORDER BY q asc
Result:
offer_id | part_id | q
1 | 1 | 1
2 | 2 | 2
4 | 3 | 4
It does not group parts and related parts (1 and 2) and returns 3 rows instead of two. How do i fix it?
UPDATE
Is it possible if i change parts table data to this?
id | part_id | group_id
1 | 1 | 1
2 | 1 | 1
3 | 3 | 1
4 | 4 | 2
I also tried this query but it doesnt group by part_id too
SELECT a.id, a.part_id, a.quantity, p.part_id AS pid
FROM supplier_offers a
INNER JOIN
(
SELECT part_id, Min(quantity) AS qty
FROM supplier_offers
GROUP BY part_id
) b ON a.part_id = b.part_id AND a.quantity = b.qty
JOIN parts p ON p.id = a.part_id
WHERE p.cross_group_uuid = '78242c22-c113-4258-806c-936de014ba10'
ORDER BY a.quantity ASC
Result from real db
UPDATE 2
It seems only way is to save part part_id in offers table and group by it

Answer 1

I don't think that this is possible, because only with as ordering you can't achieve this.
As you can see in the fiddle example you have also to add a and p.part_id is NULL
CREATE TABLE offers
(`offer_id` int, `part_id` int, `quantity` int)
;
INSERT INTO offers
(`offer_id`, `part_id`, `quantity`)
VALUES
(1, 1, 1),
(2, 2, 2),
(3, 2, 3),
(4, 3, 4),
(5, 4, 5)
;
✓
✓
CREATE TABLE parts
(`id` int, `part_id` int, `group_id` int)
;
INSERT INTO parts
(`id`, `part_id`, `group_id`)
VALUES
(1, NULL, 1),
(2, 1, 1),
(3, NULL, 1),
(4, NULL, 2)
;
✓
✓
SELECT
o.offer_id,o.part_id, o.quantity
FROM offers o
inner JOIN parts p
ON p.id = o.part_id
WHERE group_id = 1 and p.part_id is NULL
offer_id | part_id | quantity
-------: | ------: | -------:
1 | 1 | 1
4 | 3 | 4
SELECT *
FROM
(SELECT
o.offer_id,o.part_id, o.quantity
FROM offers o
inner JOIN parts p
ON p.id = o.part_id
WHERE group_id = 1
ORDER by quantity
LIMIT 1) t1
union ALL
(SELECT
o.offer_id,o.part_id, o.quantity
FROM offers o
inner JOIN parts p
ON p.id = o.part_id
WHERE group_id = 1
ORDER by quantity DESC
LIMIT 1)
offer_id | part_id | quantity
-------: | ------: | -------:
1 | 1 | 1
4 | 3 | 4
SELECT
o.offer_id,o.part_id, o.quantity
FROM offers o
inner JOIN parts p
ON p.id = o.part_id
WHERE group_id = 1
ORDER BY o.offer_ID DESC
LIMIT 2
offer_id | part_id | quantity
-------: | ------: | -------:
4 | 3 | 4
3 | 2 | 3
SELECT
o.offer_id,o.part_id, o.quantity
FROM offers o
inner JOIN parts p
ON p.id = o.part_id
WHERE group_id = 1 and p.part_id is NULL
ORDER BY o.offer_ID ASC
LIMIT 2
offer_id | part_id | quantity
-------: | ------: | -------:
1 | 1 | 1
4 | 3 | 4
SELECT
MIN(pi.offer_id),
pi.part_id,
MIN( ( SELECT pps.quantity
FROM offers AS pps
WHERE pps.offer_id = pi.offer_id
ORDER BY pps.quantity DESC
LIMIT 1
)) AS q
FROM offers AS pi
JOIN parts p ON p.id = pi.part_id
WHERE p.group_id = 1 and p.part_id IS NULL
GROUP BY part_id
ORDER BY q asc
MIN(pi.offer_id) | part_id | q
---------------: | ------: | -:
1 | 1 | 1
4 | 3 | 4
db<>fiddle here