Data Cardinality
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29-10-2019 - |
문제
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 :
The 0:M relationship occurred when there is 1 row in Contact and it's ContactID don't appear in Address.
To make the 0:M relationship Column ContactID in Table Address must be nullable.
Thanks in advance
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