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Create foreign key after normalization
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Create foreign key after normalization
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I've been creating a database, and I've just completed the normalization step. One of the relations violated the 2NF through partial dependency, so i split it into two relations, as per normalization guidelines. What i was wondering was, for the new relation that i created, does it have a foreign key that relies upon the primary key of the original relation?
For example;
Before normalization: R{PK1, PK2, attr1, attr2}
After normalization: R1{PK1, PK2, attr1} R2{PK2, attr2}
Should PK2 have foreign key with PK1?
Thanks for any help
since attr2 is functionally dependent on only PK2, attr2 has the same value for all rows that have PK2 with a given value. If you added PK1 to R2, you would have two choices, both bad.
You could have only one row in R2 for each value of PK2, in which case you are limited to one value for PK1. This overconstrains your data.
You could have many rows in R2, all with the same value of PK2 but each with a different value for PK1. Now you aren't in 2NF any more, and you're back where you started.
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