GreenSQL is an Open Source database firewall used to protect databases from SQL injection attacks. GreenSQL works as a proxy and has built in support for MySQL and PostgreSQL. The logic is based on evaluation of SQL commands using a risk scoring matrix as well as blocking known db administrative commands (DROP, CREATE, etc).GreenSQL works as a reverse proxy for MySQL connections. This means, that instead of connecting TO THE MySQL server, your applications will connect to the GreenSQL server. GreenSQL will analyze SQL queries and then, if they're safe, will forward them to the back-end MySQL server.
source:http://linuxpoison.blogspot.com/2011/02/13578167752957.html