Ensuring Data Integrity and Performance: Best Practices for Primary Key Design in SQL Server

1. Integer Data Types:
   • INT (4 bytes): Most common choice for numeric IDs with a range of -2,147,483,648 to 2,147,483,647.
   • SMALLINT (2 bytes): Suitable for smaller IDs within the range of -32,768 to 32,767, offering storage efficiency.
   • BIGINT (8 bytes): Accommodates larger numeric IDs ranging from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.

Example:

CREATE TABLE Customers (
  CustomerID INT PRIMARY KEY,
  CustomerName VARCHAR(50),
  ...
);

1. Fixed-Length String Data Types:
   • CHAR(n): Stores a fixed-length string of n characters, ensuring consistent storage size and efficient indexing. Ideal for short, fixed-length identifiers like codes (e.g., CHAR(6) for a 6-digit product code).
   • NCHAR(n): Similar to CHAR but stores Unicode characters, enabling multilingual support.

CREATE TABLE Products (
  ProductID CHAR(10) PRIMARY KEY,
  ProductName VARCHAR(50),
  ...
);

Considerations:

• Uniqueness: The primary key must guarantee unique identification for each row in the table. Choose a data type that inherently offers uniqueness or can be combined with other columns for a unique composite key.
• Performance: Integer data types generally perform better than strings in queries and indexing, due to faster comparisons and storage efficiency.
• Storage Requirements: Consider the expected number of rows and the size of the data type when choosing for optimal storage utilization.
• Business Needs: Align the data type with your business logic. For example, a customer ID might be an integer, while a product code might be a combination of letters and numbers.

Related Issues:

• Using variable-length string data types (e.g., VARCHAR) as primary keys is generally discouraged due to potential performance overhead and storage inefficiencies.
• GUIDs (Globally Unique Identifiers): While offering uniqueness, they require more storage space and might not be the most performant option for all scenarios.