Databases
MySQL
A VMS port of this OpenSource database is available.
Version 4.1.14 can be retrieved from http://www.pi-net.dyndns.org/anonymous/kits/ with everything you'll need with it.
Versions 5.1.11 and .22 can be obtained from http://www.vmsmysql.org/ (.22 contains the stable .23 version! It has been 'silently updated') (HP has now taken the lead in the maintenance of MySQL on OpenVMS, but it is targeted to Itanium and strictly 64-bit. Jean-François Piéronne, who did the basic ports up to now, will still be involved and focus on the 32-bit versions (for Alpha))
On both pages, you'll also find how to install and prepare your database.
If you have a choice, my advice would be to go for 5.1. It's far more stable, more efficient and faster than 4.1. The latter crashed quite regularly, especially under heavy load or when writing to the database after a prolonged period of inactivity, or read-only access, as much as twice a day....5.1 has been running silently for months at a time.
Multiple versions
is no problem, that is: you can have 4.1 and 5.1 side-by side, as long as each database runs on its own TCPIP port; default is 3306 (unless another value has been specified in compilation, you'll have to do so yourself...). 5.1 and 4.1 won't interfere logically either, since each has it's own root-logical: MYSQL_ROOT for 4.1, and MYSQL051_ROOT for 5.1.
Be aware that you will have to specify, in some way, what database is to be used by applications. PHPMyAdmin allows a setting (when host is not "localhost') by an extra attribute, and Wordpress has the 'normal' way of specification: adding ":<port>".
In Wordpress, for instance, you will have to define on which port the database is located, in wp-config.php. Don't forget to restart the server process that runs the PHP engine, otherwise you may think to run the new version where you actulay use the old one...
WARNING
If you use PHP as delivered by HP, be aware that the MySQL extension in the Mod_PHP package that comes with SWS, is based on MYSQL 3.1-28. It works with newer MYSQL versions but has some limitations. Building a new PHP_MYSQL extension againt a newer MySQL version is not difficult but you have retrieve the SWS source kit - and only the latest is available (discussed on http://www.pi-net.dyndns.org/piforum/viewtopic.php?t=64. One thing not mentioned there: Copy the resulting file to PHP_ROOT:[extensions]. The method I used is rename the original one (being based on 3.something) to PHP_MYSQL31.EXE, have my new file named after the MySQL version used (PHP_MYSQL41.EXE or PHP_MYSQL51.EXE) - eventually add ECO level - , and copy the required one to MPHP_MYSQL.EXE. Purge doesn't harm in that case, and you ca easily switch between versions)