Can a Foreign Key Reference a Non-Primary Key Column?

Foreign key references non-primary key column

Relating foreign keys to non-primary key columns can present challenges. In this example, the table referenced by the foreign key contains a column named "AnotherID" that is not designated as a primary key.

One possible solution is to ensure that the "AnotherID" column has a unique constraint. Books Online supports this, stating that foreign key constraints can be linked to unique constraints, not just primary keys. Modifying the table to include a unique constraint on "AnotherID" will allow the foreign key to be created.

However, it is important to consider the potential impact of such changes. Applying unique constraints may introduce additional complexities or limitations, and it is generally recommended to use primary keys as the target of foreign keys whenever possible. In situations where the data structure cannot be changed, implementing unique constraints on non-primary key columns may be a viable option to maintain referential integrity.

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