Window functions are an extremely powerful powerful part of the SQL 2003 standard, supported by most modern releases of databases such as Oracle 8+, Postgres 9.1+, SQL Server 2005+ and others. Sadly neither SQLLite or MySql seem to support them yet, but if you are working with a database where they are available, do use them: they can make your life a lot easier. Generally, with window functions, you can write simpler and faster code than you would without.
