Redundant Foreign Key

Another Database Design Mistake to Avoid is the Redundant Foreign Key.

I’ve seen a redundant FK directly to the parent, of the parent.

Redundant Foreign Key

In this example, it is the FK relationship from table Three to One.


Slightly more overhead.  Twice as many lookups when inserting into the third table.  More difficult maintenance.  Less intuitive data model.

Redundant Foreign Key - Corrected

Correct by removing the second foreign key.


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