Tuesday, 16 February 2016

Super key candidate key primary key in normalization

Keys that are used in normalization process - Define super key - Define candidate key - Define primary key - Define secondary key - Define composite key

Various keys used in the normalization process

It is the combination of two or more attributes that can uniquely identify a record within a table. There may be many super keys in a table.
Candidate KeyClick here to read more….

Candidate key is an attribute or set of attributes that can be used to uniquely identify any records in a table.
Technically, a candidate key is a minimal super key. That is, it is a super key for which no proper subset can be a key. A candidate key is a minimal set of attributes that can be used to identify a tuple (record) uniquely.
We may have many candidate keys in a table.

A primary key is one of the candidate keys of the table that is most appropriate to be the main reference key for the table. As a rule of thumb, we may try to choose the smallest among the candidate keys as the primary key.
Secondary / Alternate Key – Click here to read more….

All the candidate keys that are part of a table other than the primary key are called as secondary keys or alternate keys.
Composite Key – Click here to read more….

It is a candidate key (or primary key) that consists of more than one attribute (at least two attributes) to uniquely identify records of the table. Here, the component attributes are called prime attributes.

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