title: Datatable.Compute() returns value only when it is positive value
body: <p>I have a column(Profit Decimal(8,2) Not Null) in a table, my db is .sdf type.(Sql Server Compact). I want to sum the values of the Profit column. Sum the positive values in sumProfit and sum the negative values to sumLoss as shown in the code below</p>
  
  <pre><code>private DataTable dtbDailyOrders = MobileLine.getDailyOrdersByDate(from, to, out error);
  if (dtbDailyOrders != null)
  {
      if (dtbDailyOrders.Rows.Count &gt; 0)
      {
          bindToGrid(dtbDailyOrders);
          object sumProfit;
          sumProfit = dtbDailyOrders.Compute("Sum(Profit)", "Profit&gt;=0");
          object sumLoss;
          sumLoss =   dtbDailyOrders.Compute("Sum(Profit)", "Profit&lt;0");
          if(sumProfit == null)
          {
              // I check if it is null, but It is not null
          }
          txtProfit.Text = Convert.ToDecimal(sumProfit.ToString()).ToString("N2");
          txtLoss.Text = Convert.ToDecimal(sumLoss.ToString()).ToString("N2");
      }
  }
  </code></pre>
  
  <p>For testing I have inserted one row in my table. if value of Profit=5 the sumProfit returns 5, but if the value is -5 it returns something like this </p>
  
  <pre><code>sumProfit | {}
  </code></pre>
  
  <p>I try to check if it is null but it is not null</p>
  
  <pre><code>if(sumProfit == null)
  {
      string isNull = "the value is null";
  }
  </code></pre>
  
  <p>When I convert the sumProfit or the sumLoss I get exception error</p>
  
  <pre><code>Input string was not in a correct format.
  </code></pre>
  
  <p>can anyone please explain why it is like this.? </p>