Why would you use Oracle database?

Only Oracle and Microsoft's SQLServer are closed source, and when something goes wrong and you have a problem the answer is just a phone call away (and cash if course). Anyways MySQL and PostGre have several enterprise consulting services but in the end these consultants aren't really resposible for the product, because the product belongs to everyone. Which is great because you can go in and fix the code if you are good with C and relatively lowlevel programming, but if you aren't finding the solution might become a wild goose chase.

Now since not everyone is skilled enough, and those enterprises with money prefer the security (in the business sense) of the closed source databases, is the reason why these solutions haven't gone out of business, besides the fact that their implementations are solid and worth the money if you have it.

Ok now finally the most important difference is between SQLServer and Oracle and that difference is the OS, most people using Windows will stick with, you guessed it, SQLServer, but if you run on flavors of Unix Oracle is your closed source solution. Anyways I use Oracle on Solaris, but if our target were Windows I would probably use SQLServer because both products are rock solid, but I trust Microsoft has some special tricks under the hood to get the best performance on windows.

Just to name a few:

• Oracle Real Application Cluster - provides advanced clustering features
• Oracle Data Guard - in short provides physical and logical stand-by features.
• Oracle Exadata - implements the database aware storage (that can do predicate filtering, column projection filtering, join processing, hastens tablespace creation). The solution comes with HP servers, full 24/7 warranty, and other nice things. It's quite nice for applications with highly intensive data loading (for example thanks to the independent tablespace creation).
• Oracle Virtualization

And of course the magic of the brand ;)

And when it comes to choosing the RDBMS? Usually the choice is pretty obvious - Oracle or the rest of the world. After that you can narrow the choice down by:

• platform (windows-only or not)
• weight (sqlite, MySQL, PostgreSQL, ...)
• budget (initial license cost, maintenance + support cost)
• evolution perspectives, for example:
  • Oracle Express -> Oracle
  • SQL Server Express -> MSSQL
• business perspectives - "secure, well known product" or open-source product (bear in mind the quotation around the first phrase). Other post tends to look deeper into this aspect.

The real question is, what kind of application is going to be used to make use of a RDMS. You certainly don't need oracle for your wordpress blog or twitter clone. But if you want to do some heavy business intelligence, then Oracle might have some features which can help doing that more efficiently than the others.

Ms sql server is very good aswell, it has tons of features. If you are struck on linux and you need a database with features as offered by ms sql, then oracle would be a good pick.

I think it's because Oracle was the first RDMS that supported "sharding"

The costs of SQL Server and Oracle are not that far apart, you know.

In fact for small systems the cost of Oracle vs Your Favourite Free Database is between zero (Oracle Express Edition) and not-very-big ($5,800 processor perpetual for Standard Edition One).

Here's a link to the capabilities of the various editions in 11g: http://www.oracle.com/database/product_editions.html.

List prices are available for all territories at http://store.oracle.com -- typically large companies do not pay retail, of course ;)