Question

When using foriegn keys, I am not sure if I am suppose to use foriegn keys in two tables where it contains the same field. For example:

Option Table:

OptionId (PK auto)  OptionType
1                   A-C 
2                   A-D
3                   A-E

Question Table:

QuestionId (PK auto)  Question  OptionId (FK Option)
1                      2+2       2
2                      3+3       1

I make the OptionId in the Question Table a foreign key but am I suppose to make the OptionId in the Option Table a foreign key as well referencing to the Question Table?

Answer 1

No.

A foreign key is a constraint: it is intended to insure database integrity. You wouldn’t want someone to be able to delete an Option that a Question is joined to, as that question would no longer be valid. However, it would make perfect sense to delete a Question even though the Option it was joined to still exists — that Option may well apply to other existing or future questions.