title: Using DateDiff to find examples where table_1.column A and table_2.column B have <90 mins difference
body: <p>I am trying to find a way to filter records where the difference in two date/time fields is less than 90 minutes.</p>
  
  <p>Example:</p>
  
  <pre><code>orders.created_at = 2015-08-09 20:30:20
  table2.created_at = 2015-08-09 20:09:30
  </code></pre>
  
  <p>I have tried using TimeDiff, although I don't understand how the syntax would apply to this example.</p>
  
  <p>Data comes from separate tables both linking to the same order information. The aim is to find examples of where an order has been placed within 90 minutes, but a third field has not been updated. I would be using an <code>AND</code> query for only including results where a third field is <code>NULL</code></p>