Define candidate key, alternate key, composite key.
A
candidate key is one that can
identify each row of a table uniquely. Generally a candidate key becomes the
primary key of the table. If the table has more than one candidate key, one of
them will become the primary key, and the rest are called
alternate keys.
A key formed by combining at least two or more columns is called composite key.
A key formed by combining at least two or more columns is called composite key.
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