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

Answer 1

I would create a supertype / subtype relationship.

   THINGS
   ------
PK ThingId  

   ALPHAS
   ------
FK ThingId (not null, identifying, exported from THINGS)
   AlphaCol1
   AlphaCol2
   AlphaCol3  

   BRAVOS
   ------
FK ThingId (not null, identifying, exported from THINGS)
   BravoCol1
   BravoCol2
   BravoCol3  

   CHARLIES
   --------
FK ThingId (not null, identifying, exported from THINGS)
   CharlieCol1
   CharlieCol2
   CharlieCol3

So, for example, an alpha that has a charlie but not a bravo:-

insert into things values (1);
insert into alphas values (1,'alpha col 1',5,'blue');
insert into charlies values (1,'charlie col 1',17,'Y');

Note, you can't create more than one charlie for the alpha, as if you tried to create a two charlies with a ThingId of 1 the second insert would get a unique index/constraint violation.