Online SQL Learning

I just came across SQLZOO website and felt it very useful for quickly try and learn the SQL syntax for various DB formats including 

1. Microsoft SQL Server
2. MySQL
3. Oracle
4. DB2
5. PostGreSQL
6. IngRes

You can simply check out the default SQL syntaxes and verify them running on the fly on the sample DB tables show on the page.

Hope this will be helpful, happy SQL learning!!!