Description

Preface Database is an entity that always applies to a certain fragment of reality (the area of analysis) and constitutes a collection of data, with specified internal structure, which represents said fragment of reality and makes data retaining easier. The description the database’s inner structure is handled by data models, which allow for precise (usually formalised) depiction of the data’s properties, with the use of mathematical language, eg. relational algebra in the relational database model. Aside from describing data structures, models are also used for determining permissible data operations and as a way of imposing constraints ensuring the correctness of the database. To manage a database (understood as a collection of data), a Database Management System (DBMS) is used. It is an organised set of tools that enables the execution of operations on data that are essential for the user. So far, many database management systems (DBMS) have been developed based on various models, but those based on the relational model remain the most popular. Regardless of the choice, such software requires an understanding of the theoretical foundations of the model and the high-level language SQL (Structured Query Language). The difficulty in learning lies in the diversity and complexity of DBMS software offered by different vendors. The authors of this textbook propose learning based on PostgreSQL, one of the most popular open relational database management systems (as of 2023, according to https://db-engines.com/en/blog_post/106). For many years, this software has not fallen from the global popularity ranking of DBMS, consistently remaining in the top ten among nearly 400 DBMS of all types (the DBEngines website: https://db-engines.com/en/). The proposed textbook includes an introduction to basic SQL statements performed in relational databases, richly illustrated with examples, and tasks to be solved independently to consolidate the acquired skills. The reader will be introduced to how to create tables (basic data structures in the relational model), modify, delete and manipulate data. We will show how to improve query execution time by using indexes, while discussing selected basic issues related to the functions of the plpgSQL procedural language. In the last chapter we will present how to create a database application in Java we assume that the reader has already mastered programming skills in this language.