On the ZetCode.com site there's a five part tutorial posted about getting your PHP application up and running on a PostgreSQL database (updated on the 4th).

This is a PHP tutorial for the PostgreSQL database. It covers the basics of PostgreSQL programming with PHP. The examples were created and tested on Linux. [...] PostgreSQL is a powerful, open source object-relational database system. It is a multi-user, multi-threaded database management system. It runs on multiple platforms including Linux, FreeBSD, Solaris, Microsoft Windows and Mac OS X. PostgreSQL is developed by the PostgreSQL Global Development Group.

The chapters guide you through every step you'll need:

• An introduction to PostgreSQL and getting it and PHP support installed (with the php5-pgsql package)
• Example code showing how to extract data from your tables
• Working with images and storing their data in a table
• Pulling out the metadata from the database, things like number of rows returned and table information
• Transactions and database-side processing

In this recent post to his blog Thilanka Kaushalya shows how to use transactions in MySQL databases (using mysqli

Web applications are more popular today than ever with the increasing number of internet users. Most of the standard alone applications converted as web based applications or at least they try to provide a web interface for users. PHP and Mysql are two leading technologies which allow uses on rapid development of web based systems. "Transaction" is a powerful concept which comes with Mysql 4.0 and above versions. Lets explore that.

He introduces the concept of transactions first, providing an example of a bank transfer between two individuals. He uses this to create a simple code sample that turns off the autocommit for the connection (using mysqli_autocommit set to false) and running the SQL in order before the commit. He also includes an example of using the rollback function to return the data back to its original state if there's an error.