Originally based upon Sybase, MS SQL Server was rewritten from scratch some time ago to cope with many of the flaws of the Sybase platform. The latest version of MS SQL Server at the time of writing is SQL Server 2008, and it provides all of the features listed previous, including stored procedures and triggers.
While it does cost money, SQL Server is relatively cheap compared to Oracle, usually weighing in under $5000 per CPU. However, that does not take into account the fact that SQL Server only runs on Windows, meaning that you will have to pay the Windows licensing costs on top of the SQL Server licensing costs.
SQL Server is a very fast database when you use all-Microsoft software, however, performance has been known to decline drastically if you use anything not by MS alongside SQL Server.
Not too expensive
Requires other MS software
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