Keys in DBMS

Introduction

Keys are essential components of a database management system (DBMS) that help uniquely identify records in a table and establish relationships between tables.

Types of Keys

• Primary Key (PK): A unique identifier for each record in a table.
• Foreign Key (FK): A field in a table that references the primary key of another table.
• Composite Key: A primary key composed of multiple columns.
• Alternate Key: A column or set of columns that can uniquely identify each record in a table, but is not the primary key.
• Candidate Key: A column or set of columns that can uniquely identify each record in a table and can be used as a primary key.
• Super Key: A set of columns that can uniquely identify each record in a table, but may contain additional columns that are not necessary for uniqueness.

Primary Key Characteristics

• Uniqueness: Each record in a table must have a unique primary key value.
• Not Null: Primary key columns cannot contain null values.
• Immutable: Primary key values should not be changed once they are assigned.

Foreign Key Characteristics

• References Primary Key: A foreign key references the primary key of another table.
• Establishes Relationships: Foreign keys help establish relationships between tables.
• Maintains Data Integrity: Foreign keys help maintain data integrity by ensuring that relationships between tables are valid.

Importance of Keys

• Data Integrity: Keys help maintain data integrity by ensuring that each record in a table is unique and that relationships between tables are valid.
• Data Retrieval: Keys can be used to efficiently retrieve data from a table or to join tables.
• Data Relationships:

Keys help establish relationships between tables and ensure that data is consistent across tables.