how to use primary key and foreign key

Relational Database Design: Keys and Relationships

Primary Keys

A primary key is a unique identifier for each record in a database table. It ensures data integrity by preventing duplicate entries. Primary keys must contain unique values and cannot contain NULL values. Choosing an appropriate primary key is crucial for database performance and efficiency. Common choices include auto-incrementing integers, UUIDs, or composite keys (combinations of multiple columns).

Best Practices for Primary Key Selection

  • Keep it simple and concise.
  • Use a data type that requires minimal storage space.
  • Ensure uniqueness and non-null constraints are enforced.
  • Consider future scalability and potential for data growth.

Foreign Keys

Foreign keys establish relationships between tables in a relational database. A foreign key in one table references the primary key of another table. This creates a link between the two tables, allowing for efficient data retrieval and manipulation based on relationships. Foreign keys enforce referential integrity, ensuring data consistency and preventing orphaned records.

Types of Relationships

  • One-to-one: One record in a table relates to only one record in another table.
  • One-to-many: One record in a table can relate to multiple records in another table.
  • Many-to-many: Requires a junction table to link records from two tables, which may have multiple related records in each table.

Enforcing Referential Integrity

Database systems typically offer mechanisms to enforce referential integrity constraints. These constraints ensure that actions on a table referencing a foreign key are validated against the related table's primary key. Common actions include: preventing insertion of foreign key values that do not exist in the related table, preventing deletion of primary key values if there are corresponding foreign key references, and cascading updates/deletions to maintain consistency between related tables.

Database Normalization

Proper use of primary and foreign keys is crucial for database normalization. Normalization helps to reduce data redundancy and improve data integrity by organizing data into multiple related tables. Different normal forms (1NF, 2NF, 3NF, etc.) define levels of data organization and reduction of redundancy.