By using cascading referential integrity constraints, you can define the actions that SQL Server 2005 takes when a user tries to delete or update a key to which existing foreign keys point. Skip ...

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names a column in table-name. column-definition See column-definition. constraint-name specifies the name for the constraint being specified. referential-action specifies the type of action to be ...

Foreign keys can refer to another column in the same table. The top-level folder might need to be its own parent - I don't know if it'll let you have a NULL there.

Foreign keys enforce table relationships, for example (in the case of school enrollments) forbidding you from adding a non-existent student to a class roster, or from deleting a class roster that ...