डेटाबेस प्रबंधन प्रणाली में कुंजी प्रकार

Types of DBMS Keys

• Super Key: A set of one or more attributes that uniquely identifies a tuple in a relation.
• Candidate Key: A minimal super key, i.e., a set of attributes that uniquely identifies a tuple and cannot be further reduced.
• Primary Key: A chosen candidate key that uniquely identifies a tuple in a relation.
• Alternate Key: A candidate key that is not chosen as the primary key.
• Composite Key: A primary key composed of multiple attributes.
• Foreign Key: An attribute in a relation that refers to the primary key of another relation.

Properties of DBMS Keys

• Uniqueness: Keys must uniquely identify each tuple in a relation.
• Minimality: Candidate keys must be minimal, i.e., they cannot be further reduced.
• Irreducibility: Composite keys must be irreducible, i.e., they cannot be broken down into smaller keys.

Functions of DBMS Keys

• Uniquely identify tuples: Keys ensure that each tuple in a relation is unique.
• Enforce data integrity: Keys help maintain data consistency and accuracy by preventing duplicate or inconsistent data.
• Establish relationships: Foreign keys establish relationships between relations.
• Improve query performance: Keys can improve query performance by providing an efficient way to access and manipulate data.

Key Constraints

• NOT NULL: Ensures that a key attribute cannot be null.
• UNIQUE: Ensures that a key attribute has a unique value.
• PRIMARY KEY: Ensures that a key attribute is a primary key.
• FOREIGN KEY: Ensures that a key attribute is a foreign key that references a primary key in another relation.