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(also s control key)

Superkey definition

Superkey refers to a combination of columns that uniquely identify rows within an RDBMS (relational database management system) table. Superkeys contain several attributes that may not work independently. Combining these attributes together creates a superkey that forces every row to be unique. Superkeys are used in database design to help identify and retrieve data.

How superkeys work

A table can contain a set of columns you may want to combine and look up, for example:

  • Employee name.
  • Employee ID.
  • Address.
  • Phone number.
  • Email.

To help uniquely identify any row, we can create a superkey using all or some of these attributes. For example:

  • Employee name+Employee ID+Address+Phone number+Email
  • Employee name+Address+Phone number
  • Employee name+Employee ID+Email
  • Address+Phone number+Email

This process can be reduced by assuming that one attribute is unique (e.g., Employee ID). The superkey then becomes a single attribute (also known as candidate key).

However, using a single key does not necessarily ensure complete uniqueness. Therefore, superkeys — or combinations of several attributes — provide a better method of uniquely identifying rows.

Where superkeys may be used

  • Employee record management
  • Customer databases
  • Mailing list database

Further reading

See also: database concurrency

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