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    <p>It's hard to give general pointers without knowing the rest of your data model, but I should say this: I generally find that queries are easier to reason about when I keep them as "flat" as possible. Also, as soon as I have a bunch of null checks, I either try to add guarantees to my data, or re-pivot my query around a different "root" table.</p> <p>Anyway, <a href="http://sqlfiddle.com/#!12/41a0e/13/0" rel="nofollow">the following</a> should work for you (although I can't guarantee that it will work for any data, especially in the presence of duplicates):</p> <pre><code>select products.product_id, weeks.wkno, inventory.qoh, max(projection) from forecast join products on products.product_id = forecast.product_id join weeks on weeks.wkno = forecast.for_week left join inventory on inventory.product_id = products.product_id and inventory.asof_week = weeks.wkno group by products.product_id, weeks.wkno, inventory.qoh </code></pre> <p>Sorry I can't give you that much advice. I hope this helps.</p> <p><strong>Edit</strong>: Tweaked the query to remove the cross join. Original version <a href="http://sqlfiddle.com/#!12/41a0e/12/0" rel="nofollow">here</a>. You might want a cross join if you wanted to left join forecasts if some were missing. For your specific example it's unneeded.</p> <p><strong>Edit 2</strong>: The above query is semantically incorrect. The <a href="http://sqlfiddle.com/#!12/e7f4d/4/0" rel="nofollow">following</a> is correct, but is not as illustrative of my point.</p> <pre><code>select p.product_id, p.wkno, p.qoh, f.projection from (select products.product_id, weeks.wkno, inventory.qoh, max(forecast.asof_week) max_p from forecast join products on products.product_id = forecast.product_id join weeks on weeks.wkno = forecast.for_week left join inventory on inventory.product_id = products.product_id and inventory.asof_week = weeks.wkno group by products.product_id, weeks.wkno, inventory.qoh) as p join forecast f on f.product_id = p.product_id and f.for_week = p.wkno and f.asof_week = p.max_p </code></pre>
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    1. POin an inner join how to select only one row from the table on right based on a sliding criteria?
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    1. USJulien Langlois
    1. USJulien Langlois
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    1. COJulien, thanks, it is closer. I need not max(projection) but {projection : asof_week is most recent}. I see how you have rearranged the joins which is very insightful. +1
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      1. USDinesh
    2. COAh, sorry about that. I didn't pay attention. I'll edit.
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