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POHow to find Profit between 3 different tables
 

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    <p>My project is about a jewelery store and i try to find the produxt with the max Profit.</p> <p>I have 3 tables which gives me the info:</p> <p>SALES table:</p> <pre><code>salesid productid Quantity Price 11001 13001 4 5 11002 13002 6 10 11003 13003 5 16 . . 11012 13012 7 15 </code></pre> <p>RETURN table:</p> <pre><code>salesid productid Quantity Price 11003 13003 1 16 11007 13007 3 12 11008 13008 3 8 </code></pre> <p>PROCUREMENT table:</p> <pre><code>procurementid productid Quantity Price 100001 13001 10 2 100002 13002 10 2 . . 100012 13012 10 2 </code></pre> <p>The profit is given from this formula:</p> <blockquote> <p>Profit = Quantity * Price(Sell) - Quantity * Price(Return) - Quantity * Price(Procurement)</p> </blockquote> <p>And now here is the problem. I came up to this so far </p> <pre><code>select a.productid,(a.quantity*a.price-b.quantity*b.price-c.quantity*c.price) as Profit from sales as a ,return as b ,procurement as c where a.productid = c.productid GROUP BY productid </code></pre> <p>In this situation I don't get the correct answer.</p> <p>This is because in the return table I have only 3 registers but at the other tables I have 12, so when it calculates the profit it uses the whole return table for each row of the other tables.</p> <p>I tried to use <code>max(Profit)</code> but it didn't do anything.</p> <p>I actually don't know how I can connect the 3 registers of the return table so that they are used only when they have to. When i tried the joins a lot of rows were null. I think that something has to be done with <code>OUTER JOIN</code> or something but I don't know what to do.</p>
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