What's the best way to handle one-to-one relationships in SQL? [closed]

Answer 1

If you want each Alpha to be related to by only one Bravo I would vote for the possibility with using a combined FK/PK:

      Bravos
      --------
FK PK AlphaId
      BravoOne
      BravoTwo
      BravoThree

This way one and only one Bravo may refer to your Alphas.

If the Bravos and Charlies have to be mutually exclusive, the simplest method would probably to create a discriminator field:

      Alpha
      --------
   PK AlphaId
   PK AlphaType NOT NULL IN ("Bravo", "Charlie")
      AlphaOne
      AlphaTwo
      AlphaThree

      Bravos
      --------
FK PK AlphaId
FK PK AlphaType == "Bravo"
      BravoOne
      BravoTwo
      BravoThree

      Charlies
      --------
FK PK AlphaId
FK PK AlphaType == "Charlie"
      CharlieOne
      CharlieTwo
      CharlieThree

This way the AlphaType field forces the records to always belong to exactly one subtype.