I'm pretty sure that what I have needs to just be combined into one table, but I would still like to know when a one-to-one relationship should be used. The current system uses three Excel sheets. I just made each one into its own table and then created one-to-many relationships. I just found out that one of the tables will only have one record for each record in the main table, so I immediately thought one-to-one relationship. Then I thought why not just combine them? Combining the tables would only add two fields to the main table.
I have looked on Google to find out when one-to-one relationships should be used, but I can't find anything.