ISO/IEC 9075-2:2023

Overview - ISO/IEC 9075-2:2023 (SQL / Foundation)

ISO/IEC 9075-2:2023, Information technology - Database languages SQL - Part 2: Foundation (SQL/Foundation), is the ISO/IEC standard that defines the foundational language elements, data models and core semantics of SQL. The sixth edition (2023) specifies the baseline SQL language constructs, basic data types, operations and behaviors that ensure consistent SQL implementation and interoperability across database systems.

Key topics and technical scope

This part of the SQL standard covers the essential building blocks and behavioral rules for SQL implementations, including:

• Data types and literals: character strings, binary strings, numeric types, Boolean, datetimes, intervals, JSON types, user-defined types, row and collection types (arrays, multisets).
• Character handling and collations: repertoires, encoding forms, comparison and operations on character strings.
• Data conversions and domains: implicit/explicit conversions and domain semantics.
• Table and row models: base tables (including system-versioned and temporary tables), derived and transient tables, columns (base and generated), identity columns, table updatability and unique identification.
• Query and expression semantics: scalar expressions, table expressions, query specifications and query expression composition.
• Data analysis and windowing: group functions, window functions, aggregate functions and advanced analytical features.
• Row pattern matching: pattern definitions, partitioning, measures and row navigation semantics.
• Integrity and constraint rules: unique constraints, referential constraints, check constraints, domain constraints and assertions.
• Functional dependencies and candidate keys: formal rules for dependencies and key identification within queries and tables.
• Routines, invocation and dynamic SQL: SQL-invoked routines, externally-invoked procedures, direct invocation, descriptors, result sets and dynamic SQL concepts.
• Additional foundations: periods, collections, sequence generators, host parameters, SQL-paths and determinism rules.

Practical applications - who uses this standard

ISO/IEC 9075-2 is essential for:

• DBMS implementers and database engine vendors building SQL-compliant systems.
• Database architects and developers ensuring portability of SQL code across platforms.
• Tool and library authors (ORMs, SQL parsers, analysis tools) who need authoritative SQL semantics.
• Compliance and QA teams validating vendor claims of SQL conformance.
• Educators and technical authors teaching SQL language principles and standards-based features.

Adopting SQL/Foundation helps ensure predictable behavior for queries, consistent handling of data types (including JSON and temporal types), reliable constraint enforcement and portability of analytics and windowed queries.

Related standards

ISO/IEC 9075-2:2023 is part of the broader ISO/IEC 9075 (SQL) series. Implementers should consult other parts of the SQL standard series to cover language modules beyond the foundation (such as procedural modules, call-level interfaces and extensions).