I need to make a foreign key which will link four different types of oilfileld equipment.
The main table is called equipment, with among other things, two columns: equipment_typeFK and equipment_linkFK. These two when combined are unique.
I need to make relationships with other entities -- well, pipeline, satellite and facility.-- which are all different types of equipment. Can I not link their primary keys to the two fields of the equipment table? (MySQL doesn't like it so far.)