Lion Server: MySQL not included
Lion Server includes PostgreSQL instead of MySQL, which was included in previous versions of Mac OS X Server. If you used MySQL in a previous release and upgrade to Lion Server, you should install the latest version of MySQL or migrate your database to PostgreSQL.
Installing a new version of MySQL
If you upgraded or migrated to Lion Server from Mac OS Server v10.5 or v10.6, the installer preserved or copied the MySQL 5.0 binaries and databases. To upgrade to a more recent version of MySQL (5.1 or 5.5), follow the database upgrade steps described on mysql.com:
Note that MySQL's documentation recommends upgrading 5.0 installations to 5.1 before upgrading to 5.5. Downloads and installation instructions for MySQL are posted at the MySQL Community Edition site:
Migrating to PostgreSQL
See Apple and PostgreSQL's documentation for information about migrating your database to the OS-supplied version of PostgreSQL: