In a Database Management System (DBMS), keys are used to uniquely identify a record in a table. Different types of keys serve different purposes. Here are some key types commonly used in DBMS:
Primary Key:
Definition: A primary key is a unique identifier for a record in a table. Each table can have only one primary key, and no two records can have the same primary key value.Purpose: Used to uniquely identify records and establish relationships between tables.
Foreign Key:
Definition: A foreign key is a field in a table that refers to the primary key in another table. It establishes a link between the two tables, creating a relationship.Purpose: Used to maintain referential integrity between related tables.
Super Key:
Definition: A super key is a set of one or more columns that, taken collectively, can uniquely identify a record. It may contain more columns than necessary to uniquely identify a record.Purpose: Used in the design phase to identify unique combinations of attributes.
Candidate Key:
Definition: A candidate key is a minimal super key, meaning it is a super key with no unnecessary columns. It could be chosen as the primary key.Purpose: Identifies potential primary keys in the design phase.
Alternate Key:
Definition: An alternate key is a candidate key that was not chosen as the primary key. It is an alternative to the primary key.Purpose: Offers an alternative unique identifier for a record.
Composite Key:
Definition: A composite key is a key that consists of multiple columns to uniquely identify a record. The combination of these columns must be unique.Purpose: Used when a single column cannot uniquely identify records.
Natural Key:
Definition: A natural key is a key that is derived from the data attributes of the entity it represents. For example, a Social Security Number in a table of people.Purpose: Uses existing, inherent data as a key.
Surrogate Key:
Definition: A surrogate key is a key artificially created and assigned to a record. It has no inherent meaning or relation to the data it represents.Purpose: Provides a stable and simple primary key, especially when natural keys are complex or subject to change.
Understanding and appropriately using these key types is essential for designing a well-structured and normalized database that ensures data integrity and efficient query performance.
