Question

I have two tables, say Table A and Table B.

I want to have there to be a 1-* relationship between A and B, so for every A, there’s one specific B, and possible multiple other Bs.

So I have tables like this:

Table A
AKey INT IDENTITY PRIMARY KEY,
PrerequisiteKey INT FOREIGN KEY REFERENCES B(BKey)

Table B
BKey INT IDENTITY PRIMARY KEY,
RelationalAKey INT FOREIGN KEY REFERENCES A(AKey)

I want there to always be 1 B for every A. Should I try to do it this way (above) or should I programatically decide that the first entry in B with the A key = is the “prerequisite” B?

I’d like to be able to store that PrerequisiteKey as a separate field, but SQL doesn’t let me define tables this way because both tables need to exist before the constraints can be created.

EDIT: Or, is adding the first constraint after the tables are created the answer?

Answer 1

In these cases, you usually create the tables, then add the constraints. Use the ALTER TABLE syntax to change the FKs after creation.

ALTER TABLE A 
ADD CONSTRAINT aref FOREIGN KEY PrerequisiteKey  REFERENCES B(BKey);