Oracle is determined to keep MySQL if it acquires Sun, but the reason likely has little to do with open source and everything to do with Microsoft. Oracle doesn't compete with open source. Not really. Open source is simply a means to an end, and in the case of MySQL, a means to denting Microsoft's rising strength in emerging markets where Oracle's expensive database technology doesn't resonate.
In fact, in a recent survey by Evans Data, over 50 percent of developers in the emerging markets of China, India, Eastern Europe, and Latin America use Microsoft's SQL Server, compared to 46 percent using MySQL.
Oracle database technology? It's used, but not nearly as extensively.
MySQL gives Oracle a club with which to beat Microsoft. It's not about open source. It's about the MySQL developer community and its competitive price point, two things that Microsoft also has going for it. Arguably, though, open source provides Oracle a strong competitive differentiator against Microsoft in these markets.
Even so, I think we'll eventually see open source aiding both sides in this battle, as Microsoft learns to drop its acrimonious stance toward open source and instead strategically embrace it, as IBM, Oracle, and others have done before it.
Oracle can't afford to abandon MySQL. It's the key to unlocking its ability to effectively compete with Microsoft in tomorrow's big markets.