I've some elementary doubts regarding Foreign keys (referential integrity) :
- Can a foreign key consist of a collection of attributes - ie. can two or more columns collectively form a foreign key?
- If foreign key refers to a column within the same table, then is it compulsory that the referred column must be UNIQUE constrained?
- Can the Primary key of a column be a foreign key referring to some other relation?
Doubt related to Third Normal Form:
Is it true that 3NF is inadequate for a relation that has either:
- Multiple candidate keys
- Composite candidate keys
- Overlapping candidate keys
If possible, please provide an example.
Thank You.!