When E.F. Codd first created the formal concept of relational database management systems, he conceived of everything mathematically as sets, and made RDBMSs essentially equivalent to first-order logic. The first implementations used multi-sets instead, which removed the limits of first-order logic by allowing people to do arithmetic on aggregates.
RDBMSs quickly moved from the set-based view of the world to the more powerful multi-set-based one, but multi-sets also have limitations, or at least in terms of expressiveness and convenience of use. The next two breakthroughs were the introduction of two important new capabilities at the Data Manipulation Language level:
1. A much more flexible way to handle the concept of ordering via Windowing Functions, and
2. Views created on the fly at DML time including recursive structures via Common Table Expressions.
PostgreSQL 8.4 is the first Open Source database management system to handle lists with Windowing functions and trees and other recursive structures with SQL:2008-compliant Common Table Expressions.
You’ll learn how these work, see intriguing examples, and walk out ready to use them to your advantage.
David Fetter is based in the San Francisco Bay Area and has worked in various commercial enterprises, non-profits and educational institutions. He has worked extensively with Oracle, PostgreSQL, MySQL, Perl, PHP, PL/SQL, PL/PgSQL, PL/Perl and (of course!) vim on transaction processing and business intelligence systems.
In his free time, he brews beer, rides his bicycle, and helps run several organizations for computer professionals including the San Francisco Perl Users’ Group and the San Francisco PostgreSQL Users’ Group.
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