SQL (Structured Query Language) is a high-level language used in relational database systems. Originally developed by the IBM San Jose Research Laboratory in the late 1970s, SQL has been adopted by, and adapted for, many relational database management systems. It has been approved as the official relational query language standard by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO).

Transact-SQL, the Sybase extension of SQL, is compatible with IBM SQL and most other commercial implementations of SQL. It provides important extra capabilities and functions, such as summary calculations, stored procedures (predefined SQL statements), and error handling.

SQL includes commands not only for querying (retrieving data from) a database, but also for creating new databases and database objects, adding new data, modifying existing data, and other functions.