Beginning SQL Queries: From Novice to Professional, Second Edition

© Clare Churcher 2016

Clare Churcher, Beginning SQL Queries, 10.1007/978-1-4842-1955-3_14

2. Relational Notation

Clare Churcher¹ 

(1)Studio B Productions, Great Neck, New York, USA

Relational database theory is based on set theory.¹ When we query a database we are essentially formulating a question to retrieve a subset containing the information we require. There are two approaches for retrieving a subset of data. Relational algebra is a description of the operations to perform on the data (in the body of the book we called this the process approach). Relational calculus describes conditions that the retrieved data must satisfy (we referred to this as the outcome approach). In this appendix we introduce the formal notation to formulate queries using ...