Joe Celko's SQL for Smarties : Trees and Hierarchies

Rating:
Summary: Depth but not breadth
Review: I love and savor each of Celko?s books for their thoroughness, depth and surprises. However, with this book I am little disappointed because it showed his favorite solutions and omitted many common solutions that are better in various real-world situations. Most algorithms provided in the book are for overnight processing, not real-time update.

Omitted is the most common way hierarchies are represented in Data Warehouses using a "hierarchy bridge table". See Kimball?s book "Data Warehouse Toolkit" for more detail (yet not enough detail to give a Celko-like exploration of the topic). The bridge table solution trades away storage space for greater speed by creating a record for every path enumeration.

The book?s primary focus is on strict hierarchies. Not enough attention is given to convergent graphs and other arbitrary directed acyclic graphs, like bill of materials that reuse assemblies, where the nested sets model fails (p.164).

Also missing is maintenance of historical versions of the hierarchy, often required by financial applications.

Section 9.3 on the extremely powerful DB2 ?WITH? operator is too slim, especially since it is a SQL-99 standard and is now available with Microsoft SQL Server. If you work with hierarchies or acyclic graphs in DB2 or SQL Server take the time to learn how to use ?common subquery expressions?.

By all means if you work with hierarchies you must buy this book. No doubt the Second revison of this book will blow us away.