Gartner посчитал рынок rdbms за 2006 и по операционным системам

Software Revenue, 2006 (Millions of Dollars)

Company	2006	2006 Market Share (%)	2005	2005 Market Share (%)	2005-2006 Growth (%)
Oracle	7,168.0	47.1	6,238.2	46.8	14.9
IBM	3,204.1	21.1	2,945.7	22.1	8.8
Microsoft	2,654.4	17.4	2,073.2	15.6	28.0
Teradata	494.2	3.2	467.6	3.5	5.7
Sybase	486.7	3.2	449.9	3.4	8.2
Other Vendors	1,206.3	7.9	1,149.0	8.6	5.0
Total	15,213.7	100.0	13,323.5	100.0	14.2

По операционным системам:
Unix: 34.8%
Windows: 34.5%
Linux: 15.5%

http://www.gartner.com/it/page.jsp?id=507466