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Difference between primary key and unique key ?
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Answer Posted / tom
There is two difference between them.
1. The not null constraint is by default added to primary
key, it means, primary key attribute cannot accept null
values, whereas, the attribute declared as unique can accept
null values. It is the major difference between the two.
2. Secondly, we can have only one primary key in a relation,
whereas, multiple attributes can be declared unique at the
same time.
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