The standard MySQL's that you will see installed at most webhosting companies will not have any support for rollbacks (this requires additional configuration that isn't part of the standard Red Hat RPMs). I haven't been up on the lastest things with MySQL, but I believe that MySQL 4.0 may be adding support for subqueries, but I think triggers and views are still a ways off (version 4.1 was the last I heard).

Postgres, on the other hand, has support for all three of these features in their current version, and have had all three for quite some time.

Although I work with a heavy duty database at work on a daily basis, for my experimentation and "play" time, I use MySQL. Why? I've got a few reasons:

• most webhosts support only MySQL
• most open source web-based software supports MySQL
• the majority of books discussing web-based programming only talk about MySQL

To be honest, I don't have an opinion regarding PostreSQL since I've never used it. I'd be interested in hearing opinions from anyone who uses PostgreSQL regularly myself, especially regarding performance on a shared system.