Question

I want to have a database table that keeps data with revision history (like pages on Wikipedia). I thought that a good idea would be to have two columns that identify the row: (name, version). So a sample table would look like this:

TABLE PERSONS:
    id:      int,
    name:    varchar(30),
    version: int,
    ... // some data assigned to that person.

So if users want to update person’s data, they don’t make an UPDATE — instead, they create a new PERSONS row with the same name but different version value. Data shown to the user (for given name) is the one with highest version.

I have a second table, say, DOGS, that references persons in PERSONS table:

TABLE DOGS:
    id:         int,
    name:       varchar(30),
    owner_name: varchar(30),
    ...

Obviously, owner_name is a reference to PERSONS.name, but I cannot declare it as a Foreign Key (in MS SQL Server), because PERSONS.name is not unique!

Question: How, then, in MS SQL Server 2008, should I ensure database integrity (i.e., that for each DOG, there exists at least one row in PERSONS such that its PERSON.name == DOG.owner_name)?

I’m looking for the most elegant solution — I know I could use triggers on PERSONS table, but this is not as declarative and elegant as I want it to be. Any ideas?

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Additional Information

The design above has the following advantage that if I need to, I can “remember” a person’s current id (or (name, version) pair) and I’m sure that data in that row will never be changed. This is important e.g. if I put this person’s data as part of a document that is then printed and in 5 years someone might want to print a copy of it exactly unchanged (e.g. with the same data as today), then this will be very easy for them to do.

Maybe you can think of a completely different design that achieves the same purpose and its integrity can be enforced easier (preferably with foreign keys or other constraints)?

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Edit: Thanks to Michael Gattuso’s answer, I discovered another way this relationship can be described. There are two solutions, which I posted as answers. Please vote which one you like better.

Answer 1

In your parent table, create a unique constraint on (id, version). Add version column to your child table, and use a check constraint to make sure that it is always 0. Use a FK constraint to map (parentid, version) to your parent table.