There is a great comparison on WikiVS for those of you wondering if you should choose MySQL or PostgreSQL as your database language.
From the MySQL vs PostgreSQL page:
MySQL vs PostgreSQL is a decision many must make when approaching open-source relational databases management systems. Both are time-proven solutions that compete strongly with propriety database software. MySQL has long been assumed to be the faster but featureless of the two database systems, while PostgreSQL was assumed to be a more densely featured database system often described as an open-source version of Oracle. MySQL has been popular among various software projects because of its speed and ease of use, while PostgreSQL has had a close following from developers who come from an Oracle or SQL Server background.