title: how to convert sql union to linq
body: <p>I have the following Transact SQL query using a union.
  I need some pointers as to how this would look in LINQ i.e some examples
  wouldbe nice or if anyone can recommend a good tutorial on UNIONS in linq.</p>
  
  <pre><code>select top 10 Barcode, sum(ItemDiscountUnion.AmountTaken) from
  (SELECT d.Barcode,SUM(AmountTaken) AmountTaken
    FROM [Aggregation].[dbo].[DiscountPromotion] d
  
    GROUP BY d.Barcode
  
    UNION ALL
  
    SELECT i.Barcode,SUM(AmountTaken) AmountTaken
    FROM [Aggregation].[dbo].ItemSaleTransaction i
  
    group by i.Barcode)  ItemDiscountUnion
  
    group by Barcode
  </code></pre>
  
  <hr>
  
  <p>Note the original SQL is  <em>merging</em> the 2 selects NOT concatenating them.
  I need to know how to merge the results i.e. removing duplicates and summing  the rows amount value where there is  duplication based on bar code.</p>