Oracle Database 23c introduces a powerful new feature SQL Domains designed to help developers write less code while promoting consistency and maintainability in database design. By enabling reusable and validated data types, SQL Domains bring a new level of modularity to Oracle SQL.

What Are SQL Domains?SQL Domains are user-defined data types that include both a base data type and a set of constraints. They allow you to define once and reuse data structures particularly useful for common fields like email addresses, phone numbers, or national identifiers, which typically require consistent formatting and validation rules across multiple tables.

With SQL Domains, instead of repeating data type and validation logic throughout your schema, you can encapsulate this logic within a named domain and reference it wherever needed.

Example

Here’s how you might define a domain for email addresses:

sqlCopyEditCREATE DOMAIN email_address AS VARCHAR2(320)
CHECK (REGEXP_LIKE(VALUE, '^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$'));

This domain defines an email_address type based on a VARCHAR2(320) and includes a regular expression constraint to ensure valid email formatting.

You can then use this domain in any table definition:

sqlCopyEditCREATE TABLE users (
  user_id NUMBER PRIMARY KEY,
  email email_address
);

The email column now automatically inherits the validation logic defined in the domain.

Key Benefits of SQL Domains

• Reduce Code Duplication: Define validation logic once and reuse it across your schema.
• Enhance Maintainability: Changes to a domain propagate to all columns using it, making updates easier and safer.
• Enforce Data Consistency: Using the same domain for similar data fields ensures consistent behavior and constraints.
• Align with SQL Standards: SQL Domains are a step toward broader ANSI SQL compliance.

When to Use SQL Domains

SQL Domains are ideal in scenarios where:

• The same validation logic is applied to multiple columns or tables.
• You want to centralize business rules and data definitions.
• Schema clarity and maintainability are priorities in large-scale or long-term projects.

SQL Domains in Oracle 23c provide a structured and efficient way to define reusable data types and constraints. By minimizing boilerplate code and enhancing consistency, they represent a significant productivity boost for database developers and architects alike. As enterprise data models grow in size and complexity, features like SQL Domains will become invaluable tools in ensuring clean, maintainable, and standards-compliant schema design.