PHPMaster.com has posted the second part of their "avoid the original MySQL extension" tutorial series (part one is here). In this new part, they share more about another alternative - the PDO extension.
The PDO extension supports twelve drivers, enabling it to connect to a variety of relational databases without the developer having to learn a number of different APIs. It does this by abstracting the database interaction calls behind a common interface, enabling the developer to utilize a consistent interface for different databases. This of course gives it a major advantage over both the MySQL and MySQLi extensions who are limited to only one database.
Included in the post are examples of some of the basics - connecting, executing queries, getting the results - as well as more compelx things like binding parameters and transaction support. There's also a bit about changing the default behavior of the PDO object through config options. He finishes off the article talking some about some of the issues that could come from using an abstraction layer like this and the need to still write good, compatible SQL depending on the database.