The contents of the database cannot cause any actions, unless it is open.
At database shutdown, a script could export information to another application that could trigger the email.
Let me clarify, the query would not be the basis of the trigger.
I guess it should be that a script/trigger would be activated, say on a schedule (every day at midnight), run the query and based on what is returned, run the email script/function.
Use AppleScript and set to run in iCal... the AppleScript can open the FMP file and call a script, then close the FMP file.
Again, you set in iCal when you want the AppleScript to run.
Unfortunately, I am in a Windows environment.
Do you use an external DB? If so, you could write something like a cron job or schedule a program that make the query and sends the email. Or could could try to run a FM script on the server. The other solution would be to write a VB script that opens the FM DB, run a script and close it when finished. The VB script would be scheduled in the Windows Explorer.