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.

Result:

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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