You don't edit the SQl in the report, you right click SQl Expressions in the field explorer and select NEW.
Then Crystal inserts it into the SQL.
SQL Expressions are one of the lesser used, most powerful things in Crystal, especially in CR 8.5, you can even do correlated subqueries with them.
In your case it will just add the cast statement into the Select part of the sql, so the database does the heavy lifting.
-k