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POLast order timestamp per product
 

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    <p>I want to find the <strong>last payment</strong> (or <code>NULL</code> if n/a) made for which specified <code>product_id</code>. Below is a representation of the tables I'm working with (simplified version).</p> <pre><code>+----------+ |Products | |----------+ |product_id| +----------+ +---------------+ |Orders | +---------------+ |order_id | |order_timestamp| |order_status | +---------------+ +-----------------+ |ProductsOrdersMap| +-----------------+ |product_id | |order_id | +-----------------+ </code></pre> <p>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):</p> <pre><code>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 </code></pre> <p><strong>Edit:</strong> After PP. anwser, I ended up with the following query:</p> <pre><code>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 </code></pre> <p>Which returns</p> <pre><code>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 </code></pre> <p>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, <code>order_id</code> is wrong (<code>order_status</code> might be wrong as well).</p>
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