title: InvalidRequestError: Ambiguous column name '***' in result set, while the request is valid to mysqldb?
body: <p>My code as following:</p>
  
  <pre><code>s = DBSession()
  r = s.query(Food, FoodCategory).filter(Food.category_id == FoodCategory.id).first()
  </code></pre>
  
  <p>This query raise the exception:</p>
  
  <pre><code>sqlalchemy.exc.InvalidRequestError: Ambiguous column name 'food.category_id' in result set
  </code></pre>
  
  <p>I've tried the query directly in mysql db, and It can work well. 
  I also print the sqlalchey query. Yes, there're same lables, "food.category_id as food_category_id" and "food_category.id as food_category_id".</p>
  
  <p>I doubt that now that this query is valid to mysql, why is it not valid to sqlalchemy</p>