title: Linq - Group by multiple tables
body: <p>Using Linq to Sql how do i group the following 2 tables.</p>
  
  <p><strong>Orders Table</strong>:</p>
  
  <pre><code>CustomerID | Name   |Date            
  1          | order1 | 2010-01-01  
  2          | order2 | 2010-01-01
  2          | order3 | 2010-04-01
  </code></pre>
  
  <p><strong>Calls Table</strong>:</p>
  
  <pre><code>CustomerID | Name   |Date            
  1          | call1 | 2010-01-01  
  3          | call2 | 2010-06-01
  2          | call3 | 2010-05-01
  </code></pre>
  
  <p>I want to group the two tables by date , <strong>Result</strong>:</p>
  
  <pre><code>Date       | Orders | Calls
  2010-01-01 | 2      | 1
  2010-04-01 | 1      | 0
  2010-05-01 | 0      | 1
  2010-06-01 | 0      | 1
  </code></pre>
  
  <p>i know how to group a single table , </p>
  
  <pre><code>from o in Orders        
  group o by o.Date.Date into og
  select new {Date = og.Key,Orders= og.Count()};
  </code></pre>
  
  <p><strong>how do i group both?
  thx!</strong></p>