There is a lot more info on using PHP and mySQL together since they both grew up in the open source environment. Oracle, on the other hand, is closed source and actually costs $$$. Together that makes most "free software" (as in "free beer") people and many "free software" (as in "free speech") people shy away from it. But when it comes to needing a solid, robust, bullet-proof RDBMS, Oracle is definitely worth it.
If you are familiar with a full-featured RDBMS like Oracle, then using PHP as a frontend to it isn't that hard. Reviewing the OCI8 (and older ORA_*) section of the PHP Manual should give most experienced developers what they need to know to port their previous experience into the PHP-specifics for accessing Oracle. If you are not familiar with a full-featured RDBMS, or are only familiar with non-relational databases, then I suggest you start by learning some relational theory and SQL syntax. Oracle's TechNet website (requires free registration) might be a good place to start.
Built-in session support was the feature I was most looking forward to in PHP4. Unfortunately the project I was going to use it heavily on got "shelved" (management speak for "postponed until Hell freezes over"). I haven't worked with them as much as I would have liked to. The concepts of sessions are pretty simple. A session is created and global variables are register into it. Each page which accesses the session gets the global variables imported into its global context. Changes to the globals are saved back to the session when the page is finished.
PHP4 sessions and accessing Oracle databases from PHP are two relatively unrelated concepts. Unless of course you want to save your sessions in the Oracle database instead of saving them as disk files. In that case, there are already a couple PHP script libraries which do it.
-- Michael
Darkstreak Consulting
www.darkstreak.com
