title: Left outer join with only first row
body: <p>I have a query something like</p>
  
  <pre><code>SELECT S.product_id, S.link, C.id AS category_id
  FROM Products P
  INNER JOIN SEO S ON S.product_id = P.id AND P.product_type = 1
  LEFT OUTER JOIN Categories C ON c.product_id = P.id
  WHERE P.active = 1
  </code></pre>
  
  <p>I works fine for me as long as each product has assigned to only one category. But if a product is assigned to many categories it returns all possible combinations.</p>
  
  <p>Can I only select the first one and if a product don't have any category the link should still be returned with category_id = NULL</p>