You can read my review here:
What a pleasure to read Michael J. Hernandez's recent update to Database Design for Mere Mortals, Third Edition
I wasn't familiar with this book previously, and so had the chance to write a fresh review with no preconceived ideas from previous editions.
First, the text is well organized
Second, the examples are clear and concise
Third, the principles and underlying ideas are explained so that the reader understands not just the WHAT, but the WHY
This book is an excellent reference book for the developer who hasn't yet established a solid grounding in database design concepts. The thoroughness with which Mr. Hernandez covers the subject matter will go a long way to smoothing any gaps in one's conceptual understanding and approach to database design.