Database Modeling - Either/Or in Many-to-Many

Posted by EkoostikMartin on Stack Overflow See other posts from Stack Overflow or by EkoostikMartin
Published on 2012-08-27T21:36:42Z Indexed on 2012/08/27 21:38 UTC
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sql

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database-design

I have an either/or type of situation in a many-to-many relationship I'm trying to model.

So I have these tables:

Message
----
*MessageID
MessageText

Employee
----
*EmployeeID
EmployeeName

Team
----
*TeamID
TeamName

MessageTarget
----
MessageID
EmployeeID (nullable)
TeamID (nullable)

So, a Message can have either a list of Employees, or a list of Teams as a MessageTarget. Is the MessageTarget table I have above the best way to implement this relationship? What constraints can I place on the MessageTarget effectively? How should I create a primary key on MessageTarget table?

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