title: SQL combining 2 unique columns by random
body: <p>I need to generate diferent ads for a webpage, without them repeating.</p>
  
  <p>Lets say i have 6 zones where ads go, and 100 ads. I need to generate 6 rows with <code>banner.id</code> and <code>zone.id</code>, which will be unique every time.</p>
  
  <p>the tables:</p>
  
  <ul>
  <li><p><strong>banner_ads</strong> <code>(id, ad_location)</code></p></li>
  <li><p><strong>zones</strong> <code>(id, zone_code)</code></p></li>
  <li><p><strong>banner_to_zones</strong> <code>(banner_id, zone_id)</code></p></li>
  </ul>
  
  <p>it can be a combination of PHP and SQL if needed</p>