Preventing a table from being updated based on logic criteria

[CMorris]

I am developing an app that will be account based.  Each parent account will be able to have a set number of active users.  Each active user will be able to login under the parent account and work with the app.  The parent account admin can currently activate or deactivate a user.  Currently the admin can view a report datapage of all users and choose which ones are active.  I would like to have a way to count the number of users that are currently activated whenever a record changes and check that against what is allowed for their account.  If they have too many activated, I want to send an error message or prevent them from saving/updating the user record.  I assume I will need to do this through a triggered action whenever my user accounts table is updated, but I'm not sure how to do so.  Is this even possible?

[Hastur]

@CMorris

You can implement such a trigger.
Here you can find the example of the trigger and table design.
As the trigger has a big size? i have divided print screen in two parts

 

TABLES

TRIGGER

[CMorris]

Thank you for the quick response!  I will give this a try.

[CMorris]

That worked perfectly!  Thanks again!!!