change your select statement to be an OR (this works only for the entire erport not if you are goinmg to group on some other field in the report and look for sub totals on that group)...
Your select statement will be something like ...
(chg.opendate in start date to end date
OR
chn.close date in start date to End Date)
and {chgcat.sym} conditions here
Then conditionally count your records with formulas or Running Totals (your choice)
Open count formula
if table.opendate in startdate to enddate then 1 else 0
Sum this formula field fo get a total # of opened in range
Close count formula
if table.closedate in startdate to enddate then 1 else 0
Sum this formula field fo get a total # of closed in range
RTs will use a formual for Evaluate on as
table.open_date in startdate to enddate
table.end_date in startdate to enddate