title: Using Row Group Expressions In SSRS Causing Preview To Run Very Slow
body: <p>I have a stepped report that has 5 row groups. Each one uses an expression as the value to group on. The user selects a value for up to 5 different parameters and based on those parameters is how the report is grouped.</p>
  
  <p>With certain combinations of parameters the report may take 2min + to run in the preview pane in Visual Studio. When I deploy the report to the SSRS server the same combinations of parameters runs in 10 seconds or less. Out of curiosity, I created a copy of the report and removed the expressions from each of the row groups and specified a field to group on. In that case it previews just as fast as when viewed on the server.</p>
  
  <p>Anyone have any idea what may be going on here? </p>
  
  <p>I'm currently using Visual Studio Enterprise Update 3.</p>