Lecture Database Systems: Chapter 5 - Trần Thị Quế Nguyệt

Relational algebra serves as the foundational theoretical framework for manipulating and querying data within relational database systems, providing a precise and formal language for expressing data retrieval requests. Understanding its principles is paramount for anyone involved in database design, implementation, or optimization, as it underpins the functionality of widely used query languages like SQL. This chapter aims to introduce the core concepts and fundamental operations of relational algebra, setting the stage for comprehending how data is efficiently accessed and transformed in modern database management systems.

Sinh viên, nhà phát triển cơ sở dữ liệu, quản trị viên cơ sở dữ liệu và nhà phân tích dữ liệu đang tìm hiểu sâu về lý thuyết và hoạt động của hệ quản trị cơ sở dữ liệu quan hệ.

This chapter systematically introduces the essential operations of Relational Algebra, a cornerstone of the relational model, which enables users to specify basic data retrieval requests or queries. It categorizes these operations into several key types. Unary Relational Operations, including SELECT (σ), PROJECT (π), and RENAME (ρ), are discussed, demonstrating how they facilitate filtering tuples based on conditions, selecting specific attributes, and modifying relation or attribute names. The document then delves into Relational Algebra Operations from Set Theory, such as UNION, INTERSECTION, DIFFERENCE, and CARTESIAN PRODUCT, detailing their use in combining and contrasting relations. Furthermore, Binary Relational Operations like JOIN and DIVISION are presented, highlighting their importance in integrating information across multiple relations. Additional Relational Operations, including OUTER JOINS, OUTER UNION, and AGGREGATE FUNCTIONS (SUM, COUNT, AVG, MIN, MAX), are also covered to complete the comprehensive set of tools for data manipulation. The chapter emphasizes the 'closed' property of relational algebra, where the result of any operation is always a new relation, and illustrates how sequences of operations form relational algebra expressions. Practical examples, often using a 'COMPANY Database Schema', are provided to clarify the application of these concepts. Finally, a brief introduction to Relational Calculus offers a glimpse into alternative declarative query paradigms. Mastery of these operations is crucial for database professionals to effectively formulate and optimize complex queries.