I have a PROPERTY table and an OWNER table. I want to keep a history of who owned what property, when, and who is the current owner.
I was planning on using a third table with 4 fields. Property, Owner, Date Purchased, Date Sold. With the obvious relationships to the PROPERTY and OWNER tables. I had assumed a blank Date Sold field would allow me to indicate the current owner. However, I want to make sure I don't have active two Property/Owner relationships. That is, the same PROPERTY with an open Date Sold field for two owners.
I am not wedded to this design but I cannot think how I could do a validation for this on data entry.
This has to happen in databases all the time. How would you suggest I design or validate my way out of this?
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