The basic syntactic constructs of the structured query language SQL, used in declarative and procedural programming for modern relational database management systems Firebird, Microsoft SQL Server and Oracle Database, are examined in detail. The theoretical material is sufficiently illustrated with examples of queries and scripts for a training database, which is a simplified model of a real information system database. Additional online resources developed by the author allow the reader to independently acquire practical SQL programming skills, as well as test the acquired theoretical knowledge by completing an original laboratory workshop and testing in all sections of the textbook. The content of the textbook meets the current requirements of the Federal State Educational Standard of Higher Education. For students of higher educational institutions studying in areas related to the development, operation, administration and maintenance of relational databases of information systems, as well as for everyone who wants to independently learn the basics of SQL.