title: Symfony 3.3 EntityType using distinct values in a drop down
body: <p>I am working on an existing Symfony 3.3 project, and I have been asked to register a dropdown field in a results filter form that should contain all the values from a field in the database.</p>
  
  <p>Until now, what I have do is the following that partially works:</p>
  
  <pre><code>
  $builder-&gt;add(
      'newField',
      EntityType::class,
      [
          'class'        =&gt; Transaction::class,
          'required'     =&gt; false,
          'multiple'     =&gt; false,
          'label'        =&gt; 'New Field',
          'choice_label' =&gt; 'newField',
          'placeholder'  =&gt; 'Choose a value'
      ]
  )
  </code></pre>
  
  <p>The above code is able to display the values correctly, but unfortunately, because the table has repeatedly the same values, I get a long list of all the same values.</p>
  
  <p>Instead, what I need to achieve is to display the <code>DISTINCT</code> values from the database.</p>
  
  <p>I have tried the query_builder, but to be honest I am not sure I use it correctly as I am not an experienced Symfony developer.</p>
  
  <p>Any idea on how to display the entries of the given column with <code>DISTINCT</code> results?</p>