database - Set of Foreign Keys Where All But One Are NULL -

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What is the name of the technique to use a set of foreign keys in the table, where all the lines are given?

In other words, each line needs a foreign key for one (and only one) of a different key, so you have all the necessary foreign keys but all are the same null.

(Users of DJO can recognize it as an alternative to using a generic foreign key)

Instead, I want to create a foreign key that references a common super-table of your different parent tables.


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