Wiki of common DBMS comparison - http://en.wikipedia.org/wiki/Comparison_of_SQL_database_management_systems

Somebody comment that postgresql is less competency than MSSQL, see the comment
http://www.baubels.net/blog/?p=88

Alternative DBMS - http://www.webresourcesdepot.com/25-alternative-open-source-databases-engines/

http://blog.jooq.org/2013/10/03/the-10-most-popular-db-engines-sql-and-nosql/

http://www.xaprb.com/blog/2015/05/25/what-makes-a-solution-mature/

http://www.javacodegeeks.com/2015/07/mysql-vs-mongodb.html

Comparing major RDBMS - http://www.infoq.com/cn/articles/select-the-appropriate-rdmbs-for-the-oltp