CODEWITHSUNDEEP
sqlcomposite-key
Jared Jones
Jared Jones

Reputation: 83

Can one field in a composite key be dependent on the other?

I am thinking about making a composite key for a table of mine (which would be composed of two fields, fields A and B). However, field B is dependent on field A. Would this composite key violate any database design principles?

Upvotes: 0

Views: 624

Answers (1)

Gordon Linoff
Gordon Linoff

Reputation: 1270653

Well, yes. It does violate database design principles. Why not just use A? That is, you can always look up the value of B using a JOIN, so a composite foreign key reference is unnecessary. Storing the value of B in referring tables is redundant and inefficient (takes up space in both data pages and index pages).

There are some cases where such a foreign key is useful. You have not provided enough information to know if you have such a case. So, as a general design principle this doesn't sound right. There may be exceptions, so it is not always a bad idea.

Upvotes: 2

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