title: Linq. Query Sum on dataset
body: <p>I'm a beginner in linq.
  I would like to write this query in linq.
  Select SUM(importo), anno From(
  Select anno, Importo from[Archivio].[dbo].[AAA]
  union
  Select anno, importo From[Archivio].[dbo].[BBB]) as prova 
  group by Anno order by anno.</p>
  
  <p>I wrote this:</p>
  
  <pre><code>DataTable Tab_AAA = DS_AAA.Tables[0];
                  DataTable Tab_BBB = DS_BBB.Tables[0];
  
  IEnumerable&lt;DataRow&gt; query =
  (from A in DS_AAA.AsEnumerable()
  select A).Union(from B in DS_BBB.AsEnumerable()
  select B) 
  </code></pre>
  
  <p>now I can not enter the sum and the group by.
  Thank you all</p>