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POMySQL JOIN Tables with referenced Columns
 

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    <p>i try to get the most(30) ordered Products from the DB.</p> <p>in Table Order i have a column type its values are (1 OR -1). 1 for valid user Order, -1 for a cancellation order(in this case the order has a reference ID to the user Order) </p> <p>reference_id is an id of another Order (in the same order table)| one row referenced to another row.</p> <p>Order Table:</p> <pre><code>id | reference_id | type ---------------------------------- 1 | | 1 ---------------------------------- 2 | | 1 ---------------------------------- 3 | 1 | -1 ---------------------------------- </code></pre> <p>Products Table:</p> <pre><code>id | order_id | quantity ---------------------------------- a | 1 | 4 ---------------------------------- b | 2 | 7 ---------------------------------- a | 3 | 2 ---------------------------------- </code></pre> <p>MySQL Query: </p> <pre><code>SELECT *, sum(product.quantity) as quantity, count(*) as score FROM product LEFT JOIN order ON ( product.order_id=order.id ) WHERE (..?..) GROUP BY product.id ORDER BY score DESC LIMIT 30; </code></pre> <p>this will select, sum and count all Products in all Orders.</p> <p>BUT:</p> <p>what i am looking for is: </p> <pre><code>if(order.type &lt; 0 ){ product.quantity is in minus(-) (quantity of the Product in the referenced Order MINUS this.product.quantity) } </code></pre> <p>how to do this in the SQL Statement? i tried somany things but without success</p> <p><strong>as per comments requested Example:</strong> result should be a LIST of ordered Products grouped by product.id Most Ordered Products:</p> <pre><code>Product-id | quantity ------------------------------------------- a | 2 (in 2 Orders) ------------------------------------------- b | 7 (in 1 Order) ------------------------------------------- c | 12 (in 3 Orders) ------------------------------------------- ...etc. </code></pre> <p>many thanks</p>
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    1. CO`CASE WHEN order.type < 0 THEN (Order.quantity - product.quantity) END`. Is this what you're looking for?
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    2. COtable (Order) has no quantity as column
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    3. COok then, what do you want to subtract `product.quantity` from?
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