Today, suitable methods are known to avoid inconsistencies in data sets, allowing for optimal structuring and management of both small and large data volumes. However, there often lacks a guide that meaningfully combines these methods into a coherent and practice-oriented approach. This guide is the central theme of the present textbook. Through numerous practical examples, it is comprehensively demonstrated how relational databases should ideally be designed and how the data can subsequently be processed within the relational database. Over the past 30 years, relational databases have become a fundamental component of business information systems. However, it is anything but trivial to structure these relational databases in such a way that no inconsistencies arise during their processing.