Designing a conditional database relationship in SQL Server

Question

I have three basic types of entities: People, Businesses, and Assets. Each Asset can be owned by one and only one Person or Business. Each Person and Business can own from

Answer 1

ErikE's answer gives a good explanation on how to go about the supertype / subtype relationship in tables and is likely what I'd go for in your situation, however, it doesn't really address the question(s) you've posed which are also interesting, namely:

1. What would be the best practice for storing this type of conditional relationship in Microsoft SQL Server?
2. ...are there other options?

For those I recommend this blog entry on TechTarget which has an excerpt from excerpt from "A Developer's Guide to Data Modeling for SQL Server, Covering SQL Server 2005 and 2008" by Eric Johnson and Joshua Jones which addresses 3 possible options.

In summary they are:

1. Supertype Table - Almost matches what you've proposed, have a table with some fields that will always be null when others are filled. Good when only a couple of fields aren't shared. So depending on how different Business and People are you could possibly combine them into one table, Owners perhaps, and then just have OwnerID in your Asset table.
2. Subtype Tables - Basically the opposite of what Supertype tables are and is what you have just now. Here we have lots of unique fields and maybe one or two the same so we just have the repeated fields appear in each table. As you are finding this isn't really suitable for your situation.
3. Supertype and Subtype Tables - A combination of both of the above where the matching fields are placed in a single table and the unique ones in separate tables and matching IDs are used to join the record from one table to the other. This matches ErikE's proposed solution and, as mentioned, is the one I would favour as well.

Sadly it doesn't go on to explain which, if any, are best practice but it is certainly a good read to get an idea of the options that are out there.