SQLcompatibility
SQL compatibility refers to the degree to which a relational database management system (RDBMS) adheres to the SQL standard and supports interoperable behavior across platforms. It covers the syntax and semantics of data definition and manipulation, data types, functions, constraints, transactions, and the application programming interfaces used to access the database. Standards bodies such as ISO/IEC define successive SQL versions (for example SQL-92, SQL:1999, SQL:2003, SQL:2006, SQL:2011, SQL:2016), with newer releases adding features while preserving backward compatibility. In practice, most engines implement a substantial subset of ANSI SQL and provide vendor-specific extensions to meet performance or domain needs.
Conformance varies by engine. PostgreSQL emphasizes strong standards compliance and extensibility; MySQL aims for broad portability
For migration and interoperability, practitioners often rely on ANSI SQL as a baseline, use compatibility modes