Q: 13
Which three statements are true about defining relations between tables in a relational database?
Options
Discussion
A E. Official Oracle docs and a few practice tests both confirm this.
It’s A and E, D is the common trap since it mixes up how PK and FK relate. Seen similar in practice sets.
A/E? Had something like this in a mock. Foreign keys do allow nulls (A) and they have to match a PK or unique key when filled in (E). D is just backwards logic. Not completely sure about B, but in Oracle I think multiple nulls are possible only in certain composite unique constraints. Agree?
A and E imo. That matches what I saw in the official Oracle guide and some exam practice. Foreign keys can be null, but each value (if present) must match a PK or unique key. Pretty sure that's what they're looking for.
Option A and E make sense here. Foreign key columns can accept nulls so A is true. E is also right because every foreign key value, if not null, must match an existing primary or unique key in the parent table. C is wrong since primary keys can’t be null. D reverses the relationship. Pretty sure about this but open to corrections if I missed a nuance.
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