well SQL is the de facto language used in virtually every database. I would say all, but there may be one or more DB's out there somewhere which dont' use SQL.
Like most databases Oracle uses SQL, meaning people writing appliciation software use SQL to manipulate the db and extract data.
Although SQL was originally developed by IBM its now an internationally accepted and recognised standard (by ANSI & ISO) but virtually every manufacturer has their own variants, meaning that around 95..98% of SQL is common accross the board, each manufaturer has some variation from the standards, part of that is history (thats the way they did it prior to the standards being developed, part f that is because its a feature the manufacturer believes is a killer requirement to differentiate their product from others.
there are lots of databases that use SQL ranging from desktop DB's such as Access/JET and Filemaker through to fully blown server dbs like DB2, Oracle, SQL Server & MySQL amongst others
virtually every db can be used in virtually any application software, although it is easier using a microsoft db (such as Access or SQL Server) in a Microsoft development environment (such as Visual Studio).
Traditionally Oracle requires more DBA's and other support staff, its historyis as an alternative to DB2 and other db's running on mainframes. SQL server is and evolution / rewrite of Sybase's DB and developed primarily foruse on PC based servers.
if you want a detailed compariso between the various server products I'd suggest you do a Google
I'd rather be riding on the Tiger 800 or the Norton