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Define candidate key, alternate key, composite key?

Question Posted / sonal singhal

Answer Posted / sonal singhal

Candidate keys-> A candidate key is a combination of
attributes that can be uniquely used to identify a database
record without any extraneous data. Each table may have one
or more candidate keys. One of these candidate keys is
selected as the table primary key.

Alternate keys-> Alternate Key or Unique Key is similar to
PK ,except it accepts null Values .So that the records can
still be entered submitting null values to this attribute.

Composite keys-> compound key (also called a composite key
or concatenated key) is a key that consists of 2 or more
attributes.
A composite Key can be either Primay or Unique
Key.More then One Key columns are said to be composite keys

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