Type Constraints in 65 lines of SQL

AI summary

This article demonstrates how to extend PostgreSQL's type system by creating a custom semantic versioning (SemVer) data type. It explains how to move beyond basic composite types by implementing domain-based validation constraints, custom comparison operators, and user-defined aggregate functions to improve data integrity.

Key points

• Composite types in PostgreSQL allow for structured data storage but require additional constraints to ensure domain-specific validity.
• PostgreSQL Domains provide an effective mechanism for layering validation rules onto existing data types to make invalid states unrepresentable.
• Custom types can be made to feel like built-in types by overriding operators (like equality) and implementing custom aggregate functions.
• Offloading domain-specific logic to the database layer can significantly improve data integrity and reduce application-side IO overhead.