What is the current market share of SQL Server in the enterprise database market? Has it overcome Oracle recently?

A quick search on Google turns up the following: By revenue, Oracle database is larger than the next four combined (IBM, Microsoft, SAP, Teradata). By number of running database instances, MySQL is larger than pretty much everything else in the market combined. (Via the Sun acquisition, MySQL is also part of Oracle the company, but it's a separate team from the Oracle database.) For the  sake of full disclosure, I work at Oracle. The opinions and views expressed in this post are my own, and do not necessarily reflect the opinions or views of my employer.

I like Sten's answer the best, but there are a couple caveats to add. First, SQL Server only runs on one operating system - Windows. It's definitely the most popular on Windows, by licenses sold, by a wide margin. But MySQL is huge on Linux and Oracle is huge on Unix. So the MVP might've been mixing apples and oranges, so to speak. I think that 46% market share number is correct, but only on the Windows OS. Second, Oracle has been investing most heavily in its Financials and Apps for quite a long time. Apps has a higher R&D budget than DBMS within the company (or at least it did the last time I took a serious look at the org structure). In addition, I recall seeing a couple years ago that Oracle was earning more revenue from Support of the Oracle DBMS than on new license sales. So the majority of Oracle's total bottom line growth has been through the various packaged apps built on top of the DBMS, rather than raw sales of the DBMS itself. It makes sense in a lot of ways. It's a more expensive product that positions itself as more upscale. Those are the big players these days. DB2 is fading away and only has a toe-hold in strong IBM shops. MySQL is still quite popular in the same way that facial tissue is popular - soft, disposable, and cheap. PostgreSQL also seems to be growing in popularity on the open-source side, as well as the NoSQL platforms.

DB2, Oracle and SQL server continue to be market leaders for commercial enterprise database managers. This is reflected in the latest ranking for Dec 2015 db2-engines: http://db-engines.com/en/ranking_osvsc. SQL server is shown behind Oracle at least in popularity. If you really want to know the most running database manager then SQLite may qualify with it claiming to be running almost on "all" devices: https://sqlite.org/mostdeployed.html! But one of the meaningful ways to categorize market share actually is to see what percentage of world's business runs on a particular database. With world's top revenue companies such as Walmart, Sinopec, ExxonMobil, GM etc appear to be running DB2, significant portion of businesses is running on https://ibm.biz/ibmsdb2. To correct some facts. No DB2 is not "old". DB2 was released in 1983; Oracle in 1979. So Oracle is old but is based on relational database technology invented at IBM. Also DB2 is ahead on the cloud by being on PaaS: http://ibm.biz/db2oncloud. Yes market shares are changing. But, with columnar support released in 2010 well ahead of competition, offerings on the cloud and DB2 increasing its share where it matters, SQL server may not get the chance to go to the top. Disclaimer: I am a full time employee of IBM. Opinion my own, not IBM's.

The most interesting part of the article you are referring to(is it this one -> http://blogs.technet.com/b/in_the_cloud/archive/2013/06/06/nine-more-reasons-everyone-should-be-excited-about-the-microsoft-cloud.aspx) was that there was no information regarding the platform - Windows or Linux? SQL Server can have 46% market share on Windows (Oracle also runs on Windows), but let's also don't forget how much Unix/Linux servers we have out there that are not able to use SQL Server, but are running Oracle, for example... :)