Understanding the different types of keys and their functions is essential for designing efficient and effective database structures. This article will discuss the world of keys, exploring their definitions, purposes, and best practices for their usage.
- Surrogate keys: Artificially generated identifiers for performance optimization.
- Primary keys: Unique identifiers for records within a table.
- Foreign keys: Establish relationships between tables.
- Composite keys: Primary keys composed of multiple columns.
- Candidate keys: Potential primary keys.
What's Surrogate Key?
Surrogate keys are typically auto-incremented integer values that have no intrinsic meaning related to the entity being represented.
- They don't carry any semantic or business information about the entity.
- Often used to optimize query performance, especially for joins and indexing, as they are usually smaller and simpler to compare.
- Can decouple the primary key from the natural key, providing more flexibility in data modeling and management.
When to Use Surrogate Key?
Surrogate keys is
- Ideal for large tables with frequent inserts and updates, as they can improve performance.
- Also useful when the natural key is not suitable for primary key purposes (e.g., too long, subject to changes).
Examples of Surrogate Keys
- Scenario: A customer table with a large number of records and frequent updates.
- Surrogate Key: A unique, auto-incremented integer column named Customer_ID.
- Benefits:
- Provides a unique identifier for each customer, even if their names or other attributes are similar.
- Improves query performance, especially for joins and indexing.
- Decouples the primary key from the natural key (e.g.,
Customer_Name), allowing for changes in the natural key without affecting the primary key.
What's Primary Key?
Primary key is usually a combination of attributes that uniquely identify an entity within a business context.
- It can be a single attribute (natural key) or a combination of attributes (composite key).
- Ensures data integrity by preventing duplicate records and maintaining referential relationships between tables.
- Often reflects business rules and constraints.
When to Use Primary Key?
Primary keys is
- Suitable when the natural key is a good representation of the entity and meets the requirements for a primary key (unique, non-null, and immutable).
Examples of Primary Keys
- Scenario: A product table with a small number of records and infrequent updates.
- Primary Key: A combination of columns named Product_ID and Version_Number.
- Benefits:
- Represents the unique identity of a product based on its identifier and version.
- Ensures data integrity by preventing duplicate products with the same identifier and different versions.
- Reflects the business rules and constraints of the product entity.
What's Composite Key?
Composite key is a primary key composed of multiple columns.
- Uniquely identifies records when a single column is insufficient
- Can be a primary key or a unique constraint
When to Use Composite Key?
- When a single column cannot uniquely identify records
- To represent a composite entity
Examples of Composite Keys
(Order_ID, Product_ID) in an Order_Items table(Customer_ID, Order_Date) in a Customer_Orders table
What's Foreign Key?
Foreign key is a column or set of columns in one table that references the primary key of another table.
- It's used to establishe relationships between tables
- Enforces referential integrity
- Can be a single column or a composite key
When to Use Foreign Key?
- Modeling relationships between entities
- Ensuring data consistency
Examples of Foreign Keys
Customer_ID in an Orders table referencing the Customer_ID in a Customers tableProduct_ID in an Order_Items table referencing the Product_ID in a Products table
What's Candidate Key?
Candidate key is a unique combination of columns that can uniquely identify a record within a table.
- Can be a primary key
- Identifies potential primary keys
- Can be used for unique constraints
When to Use Candidate Key?
- Identifying potential primary keys
- Creating unique constraints
Examples of Candidate Keys
Email in a Customers table(First_Name, Last_Name, Birthdate) in a Employees table
Additional Notes:
- A table can have only one primary key, but it can have multiple candidate keys.
- A foreign key can reference a primary key or a unique constraint.
- A composite key can be a primary key or a unique constraint.
Conclusion
The choice between keys depends on the specific needs of the database design, considering factors like data volume, update frequency, and business rules.