Sun, Oracle’s sometimes best friend, turned into an Oracle competitor this morning when it said it was buying MySQL, the open source database that’s part of the famous LAMP stack. It’s paying a billion dollars.

MySQL was supposed to go public this year but picked the easier monetization route.

Sanford C. Bernstein estimates MySQL’s financial position at breakeven on $60 million-$80 million on trailing 12-month revenues although over 100 million copies of the database have been downloaded.

Sun is paying $800 million cash for MySQL’s stock and assuming about $200 million in options. But Sun has been known to overpay for acquisitions before. Remember its fatal $2 billion Cobalt Networks deal?

Sun, which is given to highfalutin rhetoric, sees its acquisition of MySQL as reaffirming its position “at the center of the web economy” and its role as “the largest commercial open source contributor.”

CEO Jonathan Schwartz said the deal was “all about growth,” both MySQL’s and Sun’s, and “better value to shareholders.”

In a canned statement, he said, “Acquiring MySQL amplifies our investments in the technologies demanded by those driving extreme growth and efficiency, from Internet media titans to the world’s largest traditional enterprises. MySQL employees and culture, along with its near-ubiquity across the web, make it an ideal fit with Sun’s open approach to network innovation. And most importantly, this announcement boosts our investments into the communities at the heart of innovation on the Internet and of enterprises that rely on technology as a competitive weapon.”

Most MySQL deployments are on Linux. Solaris only comes in behind Windows at 20% and 75% of those Solaris deployments aren’t on Sun hardware.

Sun evidently has hopes of changing that equation and moving more Sun servers, storage and software on the back of MySQL – particularly since, it says, “Sun customers are deploying MySQL at a phenomenal rate” – but then it also talks about continuing to support and invest in PostgresSQL and Oracle as well as JavaDB. “We can support them all,” Schwartz said.

LAMP stack aficionados now have to worry about where MySQL optimization will go.

Sun is already talking about MySQL, OpenSolaris and Java – along with its Glassfish app server and NetBeans IDE – being a “powerful web application platform across a wide range of customers shifting their applications to the web.”

Sun also expects to drive MySQL, which is currently used by such as Internet biggies as Google, Facebook and Baidu, into more traditional applications and enterprises and “change the landscape of the software industry.”

In part it’s supposed to do this by piggybacking on Sun’s distribution channels and OEM relationships with Intel, IBM and Dell.

Sun means to drive it into large mission-critical applications, where, it says, the database has found little adoption – largely because it wasn’t designed for them.

However, as Richard Green, the head of Sun’s software operation, said, since MySQL version 5 a couple of years ago, the database has had a “pluggable” character capable of adding different kinds of functionality – like, say, relational widgetry – that appeals to different customer sets. That facility, of course, makes it more competitive with Oracle. And Sun expects to push its performance, scaling and integration roadmap.

Sun described its integration of MySQL as extending the database’s commercial appeal and improving its value proposition with the addition of Sun services. There have been reports of MySQL users bypassing MySQL support for cheaper, consolidated third-party support from outfits like OpenLogic.

MySQL CEO Marten Mickos, who’s going to stick around and report to Green, said the acquisition makes “wonderful sense,” ticking off its attributes as “better service, a full stack and new customers.”

Green, by the way, thinks that the Sun-MySQL tie-up has more synergy than other Sun acquisitions.

The acquisition is expected to close sometime between now and early in the second calendar quarter.