CODEWITHSUNDEEP
databaserelational-databaserelationshipcardinality
Agus Syahputra
Agus Syahputra

Reputation: 446

Data Cardinality

I'm confusing about 0:M relationship.

So, I want to ask about that.

Assumes we have 2 tables :

Contact which has attributes like : ContactID(PK), Name

Address which has attributes like : AddressID(PK), Desc, ContactID(FK to Contact, Nullable, Not Unique)

Is my statement right that :

Thanks in advance

Upvotes: 0

Views: 368

Answers (1)

Tobu
Tobu

Reputation: 25436

  • The 0:M notation is used to annotate one side of a relationship, indicating its cardinality. It is a range and is accurate in every instance of the relationship. When ContactID doesn't occur in address, the cardinality is 0.

  • Foreign keys don't need to be nullable, and shouldn't in general. The 0 case still happens, when a ContactID occurs in Contact and not Address.

Upvotes: 1

Related Questions