Sorry, I don't join tables in CR, so I am not familar with which way it goes. What the SQL
should look like is:
SELECT ...
FROM Users
LEFT OUTER JOIN Pr_transactions ON Users.UserID = Pr_transactions.UserID
LEFT OUTER JOIN Cp_transactions ON Users.UserID = Cp_transactions.UserID
You know that you have users, and they may or may not have printed/copied anything. You can always filter out the users that have not copied or printed, but you can't do it the other way around. The Left joins, what is to the left of the word join, forms the base table, and if it is not the user, then you will be limiting and or omitting the people that copied.
Check the SQL syntax and see if the joins are as expected.
good luck