title: SSRS 2008 R2 - evaluating running total only on change of group
body: <p>I have a report where I capture patient information, some of which is stored in the patient table and some of which is stored in the observations table. Taking date of birth as my example, if I count all the records for which the DOB has been supplied, I get significantly more than the total number of patients, because of the join to the observations table. How do I evaluate the running total only once for each group?</p>
  
  <p>Edit: some sample data over at <a href="http://sqlfiddle.com/#!3/27b91/1/0" rel="nofollow">http://sqlfiddle.com/#!3/27b91/1/0</a>. If I count birthdates from that query, I want 2 as the answer; same for race and ethnicity.</p>