Different Type of keys in Database Managemenet System.



All super, candidate and primary, secondary keys are used to uniquely distinguish all rows in data base. But the main difference between them is.


  • Super 🔑-superset of candidate keys
  • Candidate 🔑-subset of super key, it is a single key or least combination of feild that uniquely  identifies every tuple.
  • Primary 🔑- it is a candidate key that is most appropriate to become main key for the table.
  • Secondary 🔑-candidate keys which are not selected as primary keys.



  • Non-key attributes (attributes other than candidate keys)
  • Non prime attributes (attributes other than primary key)




Foreign 🔑??


  • It is a feild in one table that uniquely identifies a row in another table
  • They are constraints between column of tables.

Example:





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