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PORandom record from maximum set (with an additional constraint)
 

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    <p>Two tables, products and producers. I would like to buy a particular type of product, but only from the highest priority producer that makes it, and I need their URL. If multiple producers have the highest priority, then give each producer and equal chance of being selected.</p> <p>I decide to buy a car for example. From the sample data below, Honda and Ford are the cars with the the highest priority, so return a Honda URL 50% of the time and the Ford URL 50%.</p> <pre><code>Products Table: | producer_id | product_type | product_url | |-------------|--------------|-----------------| | 3 | car | wiki.com/a.html | | 1 | bat | wiki.com/b.html | | 2 | car | wiki.com/c.html | | 4 | car | wiki.com/d.html | | 2 | car | wiki.com/e.html | Producers Table:| producer_id | producer | priority | |-------------|----------|----------| | 1 | wilson | 30 | | 2 | honda | 20 | | 3 | mazda | 5 | | 4 | ford | 20 | </code></pre> <p>The mess I have at the moment I'm sure can be simplified:</p> <pre><code>SELECT products.url FROM products, producers WHERE products.producer_id = producers.producer_id AND products.product_type = 'car' AND priority IN (SELECT MAX(priority) FROM products, providers WHERE products.producer_id = producers.producer_id AND products.product_type = 'car' ) ORDER BY RAND() LIMIT 1 </code></pre> <p>plus it has the problem where it will return Honda's pages 2/3rds of the time because Honda has two models of the three with highest priority. </p> <p>Looking forward to learning something!</p>
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