title: Crystal Reports. How do I show amount of records between 2 optional dates
body: <p>I'm new to Crystal and I have to create a basic report that requires 2 input optional parameters: <code>DateStart</code> and <code>DateEnd</code>. 
  Report shall include amount of records in a table beetween 2 dates (if <code>DateEnd</code> date value is missed report shall consider that it requires all records no matter how old they are. If <code>DateStart</code> is missed report shall consider it requires all records no matter how young they are) </p>
  
  <p>I guess I'll have to use <code>SQL Expression Field</code> but can't figure out how to implement where clause. </p>
  
  <p>How would you implement such a report? </p>
  
  <p>Thank you in advance! </p>