I have a database with a primary key that identifies the patient uniquely. This number is used in 15 other tables with extensive data about the SAME patient. Each of these tables is I think a one to one relationship, but what do you call it when their are extensive tables with details about the same patient? Does the primary key act as a foreign key. When I enterred the same number again as a primary key I was told I had enterred duplicate information despite the fact that it was in a different table.

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Reply from Richard Rost:

The PRIMARY key would in be whichever table you have your Autonumber set. If you're not using an Autonumber (which I don't recommend) then you could, in theory, have multiple primary keys... which may complicate your database.