title: crystal report use Maximum as Sum condition problem
body: <p>I met a problem with sum function:
  the data have a datetime column and I want to get sum of who's datetime is max. And also there's anoher group condition.
  So I do like:</p>
  
  <ol>
  <li>Add formula maxDatetime: Maximum({datetime}, {groupcondition})</li>
  <li>Add new formula for sum ValueToSum: if({datetime} = {@maxDatetime}) then value else 0</li>
  <li>Sum the value, add new formula totalValue: Sum({@valueToSum}, {groupcondition})</li>
  </ol>
  
  <p>The result is the sum can't be processed, it says: 'valueToSum can't be sumed'.</p>
  
  <p>I think the causor may be using a maximum value as a condition in step 2. Because when use 1 = 1 to replace the condition, there's no problem.</p>
  
  <p>Can anyone give some advice?</p>