Define candidate key, alternate key, composite key?
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Answer Posted / mona
A set of fields that uniquely identifies a tuple according
to a key constraint is called candidate key for the relation.
(1)No two values of keys are same
(2)the set of fields{sid,sname} is not a key for
students,because this set properly contains the key{sid}.
The set {sid,sname} is an example of a super key,which is a
set of fields that contains a key.
EX:
create table customer(customer_name char(20),street
char(30),city char(30),primary key(customer_name));
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