Because of its stability and security options, people have chosen Oracle over the other two large competitors. Over 60% of all SAP customers have chosen the Oracle databases, and this has worked fine for a number of years. Now however, SAP has chosen to change the way the database market works.
For the longest time Oracle has ruled the market with its huge customer base and its ability to deliver a system that is nearly foolproof. It can provide options that the other databases simply cannot. But it may have done something slightly foolish as well. Oracle chose to acquire various resources such as PeopleSoft, Siebel Systems, and a few others, but instead of merging these companies right away to make it more manageable, Oracle has dragged its feet trying to decide whether or not this is the best move for them.
While Oracle tries to figure out its place in the universe SAP has put their heads together with IBM and its massive DB2 project, which is code-named Viper. This software is optimized for SAP and there are features that will boost SAP application performance making it preferable for those who use SAP in their own businesses.
While this will prove to be beneficial for SAP and the customers of SAP it could deal a devastating blow to Oracle since the majority of its customers use the database for SAP applications. It will also deal a blow, though not as severe to Microsoft SQL database, though that particular database is used more for other things besides SAP application deployment.
No one knows for sure what will happen in the future; for now Oracle is still around and all is well in the world, but in the fast moving corporate world things can change in an instant, and if you blink it could all be gone. Keep an eye on this feud because you never know exactly what it might erupt into in the future.