Define candidate key, alternate key, composite key?
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Answer Posted / sonya jalil khan
candidate key:if it qualifies to uniquely select a specific
row in the table such that the data in that table depend
completely on that key and nothing else is required.the
candidate key cannot hold NULLS.the candidte key should
never change it must holds the same value for a given
occurence of an entity for the lifetime of that
entity.
example:
EMP ID , NAME,JOB,DEPARTEMENT ID
here emp id is a candidate key.becouse a minimal set of
columns that can be used to identify a single row
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