The basics of database theory, methods and algorithms used in the implementation of database management systems, as well as the features of these methods and algorithms implemented in PostgreSQL DBMS are presented. The material of the book forms the basis for the basic training course and contains a brief overview of the requirements and criteria for evaluating DBMS and databases, a theoretical relational data model, basic constructions of the SQL query language, organization of access to the PostgreSQL database, application design issues and basic extensions available in the PostgreSQL system. Course is designed for junior students (undergraduate) classical and technical universities, as well as other universities with basic programming training and continuing to specialize in areas close to programming.