Define candidate key, alternate key, composite key?
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Answer Posted / shreyas joshi
Candidate key- A candidate key is defined as an attribute or
set(combination) of attributes that no 2 tuples(rows) in a
relation hold duplicate values of it.or we can say that a
candidate key is a kind of superkey, if whose subset taken
than it cannot be said as a superkey..in otherwords consider
a customer table with attributes(cust_id,cust_name,cust_street).
than candidate key is (cust_name,cust_street)(combination)
Now this is sufficient to uniquely identify an entity in a
table.But if its subset taken i.e alone cust_name or
cust_street, they individually cannot identify uniquely a
tuple or entity..IN short a candidate key is a superkey with
no super key as it subsets.
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