title: Sum of a particular column using LINQ
body: <p>Using the below mentioned query I am getting the all the values of a column called 
  <strong>promotionValue</strong> . I want to get the sum of all the values of *<em>matched *</em></p>
  
  <pre><code>var matched = from table1 in dvtempPropertyRoomRatePromotion.ToTable().AsEnumerable()
                join table2 in dvPropertyRooms.ToTable().AsEnumerable() on
                table1.Field&lt;DateTime&gt;("RateDate") equals table2.Field&lt;DateTime&gt;("RateDate")
              where table1.Field&lt;DateTime&gt;("RateDate") == table2.Field&lt;DateTime&gt;("RateDate")
                 select table1.Field&lt;string&gt;("promotionValue");
  </code></pre>