Send an alert to a user when activity assigned to them?

Hello all

We would like an alert to be triggered and sent to a user every time a new activity is assigned to them. We have multiple users and multiple people entering the activities. I know this is possible by writing a query/alert for every single user, but is it possible to write one query whereby each user gets notified when an activity is assigned to them? Help would be appreciated....

Many thanks

Wendy