Last order timestamp per product - mysql

Question

I want to find the last payment (or NULL if n/a) made for which specified product_id. Below is a representation of the tables I'm working with (simplified version).
+----------+
|Products |
|----------+
|product_id|
+----------+
+---------------+
|Orders |
+---------------+
|order_id |
|order_timestamp|
|order_status |
+---------------+
+-----------------+
|ProductsOrdersMap|
+-----------------+
|product_id |
|order_id |
+-----------------+
After JOINs, MAXs, GROUP BYs, LEFT JOINs, multiple INNER JOINs to get the greatest-n-per-group, I still can't get to the right result. Most of the times, products with multiple orders are returning multiple rows. The best results I got so far were (I was searching specific products):
product_id order_id order_timestamp order_status
8 NULL NULL NULL
9 NULL NULL NULL
10 NULL NULL NULL
12 NULL NULL NULL
13 NULL NULL NULL
14 11 2013-08-13 07:22:01 finished
15 11 2013-08-13 07:22:01 finished
15 12 2013-08-14 00:00:00 finished
32 11 2013-08-13 07:22:01 finished
83 9 2013-08-13 07:04:02 finished
83 10 2013-08-13 07:11:42 finished
Edit: After PP. anwser, I ended up with the following query:
SELECT p.product_id, o.order_id, MAX(order_timestamp) AS order_timestamp, order_status
FROM Products p LEFT JOIN (ProductsOrdersMap m, Orders o)
ON (p.product_id = m.product_id AND m.order_id = o.order_id)
WHERE p.product_id IN (8,9,10,12,13,14,15,32,83)
GROUP BY p.product_id
Which returns
product_id order_id order_timestamp order_status
8 NULL NULL NULL
9 NULL NULL NULL
10 NULL NULL NULL
12 NULL NULL NULL
13 NULL NULL NULL
14 11 2013-08-13 07:22:01 finished
15 11 2013-08-13 07:22:01 finished
32 11 2013-08-13 07:22:01 finished
83 9 2013-08-13 07:04:02 finished
At first glance, it seems correct but only the products IDs and the timestamps are right. Comparing the two queries above, you can see that, for products 15 and 83, order_id is wrong (order_status might be wrong as well).

Answer 1

This query should return the specified resultset (this is only desk checked, not tested)
to return ALL product_id
SELECT p.product_id
, m.order_d
, m.order_timestamp
, m.order_status
FROM products p
LEFT
JOIN ( SELECT kl.product_id
, MAX(ko.order_timestamp) AS latest_timestamp
FROM orderproductsmap kl
JOIN orders ko
ON ko.order_id = kl.order_id
GROUP
BY kl.product_id
) l
ON l.product_id = p.product_id
LEFT
JOIN ( SELECT ml.product_id
, mo.order_id
, mo.order_timestamp
, mo.order_status
FROM orderproductsmap ml
JOIN orders mo
ON mo.order_id = ml.order_id
) m
ON m.product_id = l.product_id
AND m.order_timestamp = l.latest_timestamp
GROUP
BY p.product_id
The inline view "l" gets us the latest "order_timestamp" for each "product_id". This is joined to inline view "m" to get us the whole row for the order that has the latest timestamp.
If there happens to be more than one order with the same latest "order_timestamp" (i.e. order_timestamp is not guaranteed to be unique for a given product_id) then the outermost GROUP BY ensures that only one of those order rows is returned.
If only particular product_id values need to be returned, add a WHERE clause in the outermost query. For performance, that same predicate can be repeated in the inline views.
to return only SPECIFIC product_id we add three WHERE clauses:
SELECT p.product_id
, m.order_d
, m.order_timestamp
, m.order_status
FROM products p
LEFT
JOIN ( SELECT kl.product_id
, MAX(ko.order_timestamp) AS latest_timestamp
FROM orderproductsmap kl
JOIN orders ko
ON ko.order_id = kl.order_id
WHERE kl.product_id IN (8,9,10,12,13,14,15,32,83)
GROUP
BY kl.product_id
) l
ON l.product_id = p.product_id
LEFT
JOIN ( SELECT ml.product_id
, mo.order_id
, mo.order_timestamp
, mo.order_status
FROM orderproductsmap ml
JOIN orders mo
ON mo.order_id = ml.order_id
WHERE ml.product_id IN (8,9,10,12,13,14,15,32,83)
) m
ON m.product_id = l.product_id
AND m.order_timestamp = l.latest_timestamp
WHERE p.product_id IN (8,9,10,12,13,14,15,32,83)
GROUP
BY p.product_id
Only the WHERE clause on the outermost query is required. The other two are added just to improve performance by limiting the size of each of the derived tables.

Answer 2

SELECT
P.product_id
,MAX(order_timestamp)
FROM
Products P
,Orders O
,ProductsOrdersMap M
WHERE
P.product_id = M.product_id
AND O.order_id = M.order_id
GROUP BY
P.product_id

Answer 3

To return all products, even those without orders, a LEFT JOIN is definitely the way to go. The answer from #PP above uses "old-style" inner joins and is equivalent to this:
SELECT
P.product_id
,MAX(order_timestamp)
FROM Products P
INNER JOIN ProductsOrdersMap M ON P.product_id = M.product_id
INNER JOIN Orders O ON O.order_id = M.order_id
GROUP BY
P.product_id
Starting with this syntax it's a lot easier to get to the LEFT JOIN - just replace INNER with LEFT:
SELECT
P.product_id
,MAX(order_timestamp)
FROM Products P
LEFT JOIN ProductsOrdersMap M ON P.product_id = M.product_id
LEFT JOIN Orders O ON O.order_id = M.order_id
GROUP BY
P.product_id
Addendum: Renato needed something more than just reworking the other answer as a LEFT JOIN because the order_id and order_status have to come along with the maximum timestamp. The easiest approach is to start with a list of product ID's and order ID's where the order has the maximum timestamp by order_id:
SELECT
p2.product_id,
o2.order_id
FROM Products p2
INNER JOIN ProductsOrdersMap m ON p2.product_id = m.product_id
INNER JOIN Orders o2 ON m.order_id = o2.order_id
WHERE (o2.order_id, o2.order_timestamp) IN (
SELECT order_id, MAX(order_timestamp)
FROM Orders
GROUP BY order_id)
Then, instead of using ProductsOrdersMap to resolve products to orders, use the results from the query above:
SELECT
p.product_id,
o.order_id,
o.TS,
o.order_status
FROM Products p
LEFT JOIN (
SELECT
p2.product_id,
o2.order_id
FROM Products p2
INNER JOIN ProductsOrdersMap m ON p2.product_id = m.product_id
INNER JOIN Orders o2 ON m.order_id = o2.order_id
WHERE (o2.order_id, o2.order_timestamp) IN (
SELECT order_id, MAX(order_timestamp)
FROM Orders
GROUP BY order_id)
) MaxTS ON p.product_id = MaxTS.product_id
LEFT JOIN Orders o ON MaxTS.order_id = o.order_id