title: Select only one column from mnesia
body: <p>how can i select only one column from mnesia?
  I can select onle column in ets table with this code:</p>
  
  <pre><code>ets:match(AllData_TableId, {'_', '$1','_',','_'},3),
  </code></pre>
  
  <p>I need something similar for mnesia.</p>
  
  <p>Thank you.</p>