Ok, just to quickly fill you in. I have an equipment table. Also have another table to note the users on that piece of equipment.

As the users chage regularly I need to be able to delete them off that piece of equipment. Intially to do this i had a on delete set null. This isn't really feasable as the primary key of equipment_id shouldn't ever be null. Other than leaving the relationship out im not sure what to do.

Is there another way to do this? Im using MySQL, can I use triggers.

Thanks for looking.