Different types of Keys in DBMS

There are 7 keys in DBMS

Primary Key

  • Key which is used to identify one and only instance of entity uniquely. An Enity can contains multiple keys, and keys which is most suitable becomes the primary key.
  • For each entity the primary key selection is based on requirements and developers.

Candidate Key

  • A key or an attribute that uniquely identifies a tuple is called Candidate key.
  • Apart from primary key, other keys are considered as candiate key.
  • The candidate keys are as strong as the primary key.

Super Key

  • An attribute set that can uniquely identify a tuple is called as Super Key. It is a superset of candidate key.

Foreign Key

  • Column of table that is used to point the primary key of another table is called as Foreign key.

Alternate Key

  • One of more attributes or a combination of attributes that uniquely identifies a tuples in a relation is called Alternate Key.
  • These attributes or combinations of the attributes are called the candidate keys.
  • One key is chosen as primary key and the other keys remain as candidate keys if they exist and is called as alternate keys.
  • Total number of alternate keys is the total number of candidate keys minus the primary key.
  • In a relation if there is only one candidate key alternate keys may or may not exist.

Composite Key

  • Whenever there is more than one attribute in a primary key, it is known as Composite key or concatenated key.

Artificial Key

  • Keys that are created using arbitarily assigned data is known as artificial keys.
  • When primary key is large and complex and has no relationship with other relations, then the artificial key is created.
  • Data values of an artificial key are usually numbered in serial order.
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