title: Sequelize group by with association includes id
body: <p>So when requesting a group by from sequelize as follows:</p>
  
  <pre><code>return models.WorkingCalendar
              .findAll({
                  attributes: [
                      'WorkingCalendar.PeriodId',
                      'WorkingCalendar.date',
                      'Period.name'
                  ],
                  include: [
                      {
                          model: models.Period,
                          attributes: []
                      }
                  ],
                  where: {
                      GetSudoId: currentGetsudo.id,
                      UnitPlantId: unitPlantId
                  },
                  group: ['WorkingCalendar.PeriodId',
                      'WorkingCalendar.date',
                      'Period.name'],
              });
  </code></pre>
  
  <p>Sequelize will run this query:</p>
  
  <pre><code>SELECT 
  [WorkingCalendar].[id],
  [WorkingCalendar].[PeriodId], 
  [WorkingCalendar].[date], 
  [Period].[name] 
  FROM [WorkingCalendars] AS [WorkingCalendar] 
  LEFT OUTER JOIN [Periods] AS [Period] ON [WorkingCalendar].[PeriodId] = [Period].[id] 
  WHERE [WorkingCalendar].[GetSudoId] = 1 AND [WorkingCalendar].[UnitPlantId] = N'1' 
  GROUP BY [WorkingCalendar].[PeriodId], [WorkingCalendar].[date], [Period].[name];
  </code></pre>
  
  <p>Yet I never asked for the <code>WorkingCalender.id</code> and I cannot seem to get rid of that.
  How do I make sure sequelize is not getting me this <code>id</code> from the <code>workingCalendar</code>?</p>
  
  <p>I've already found that for associations the attributes should be an empty array and that works but not for the main object since I need only 3 columns.</p>