Hopefully a simple question, but I don't have much experience with writing contraints in SQL Server.

I have one table called Folders with an ID field (autonumber PK) and a Folder field (varchar unique). This contains a list of folders.

I have a second table called Queue. It has several fields, one of which being Folder (corresponds to the Folder field in the first table). How do I write a constraint to enforce that the contents of the Folder field in the Queue table exists in the Folder field in the Folders table?

Thanks!