title: MongoDB and "joins"
body: <p>I'm sure MongoDB doesn't officially support "joins". What does this mean?</p>
  
  <p>Does this mean "We cannot connect two collections(tables) together."?</p>
  
  <p>I think if we put the value for <code>_id</code> in collection A to the <code>other_id</code> in collection B, can we simply connect two collections?</p>
  
  <p>If my understanding is correct, MongoDB can connect two tables together, say, when we run a query. This is done by "Reference" written in <a href="http://www.mongodb.org/display/DOCS/Schema+Design" rel="noreferrer">http://www.mongodb.org/display/DOCS/Schema+Design</a>.</p>
  
  <p>Then what does "joins" really mean?</p>
  
  <p>I'd love to know the answer because this is essential to learn MongoDB schema design. <a href="http://www.mongodb.org/display/DOCS/Schema+Design" rel="noreferrer">http://www.mongodb.org/display/DOCS/Schema+Design</a></p>