Let's say I'm designing an employee database for a secret spy agency. This agency has all different kinds of employees (spies, janitors, middle managers, etc), all of which need to be in the db. Each kind of employee has its own fields, so each kind of employee needs to have its own table.
For example: On the "spies" table, the fields might be "primary weapon," "current location," "kill count," etc. But for middle managers, the fields could be "department" and "budget."
But ALL employees need to have a "panic phrase" that is unique to them (in case they're captured and can only get a single word out to the agency). I can't have a unique "panic phrase" field in each table, because that could allow for duplicate panic phrases in different tables.
I could put all the panic phrases in their own table and just have a "panic_id" field in the employee tables, but then we have the same problem: two employees on different tables could point to the same panic phrase id.
How do I design the database to make this work? Or is there no solution, other than checking each field in each table?