Need help to learn Codeigniter with Database

hi all,

I am trying to dive into Codeigniter and knew without the help of official Documentation and experts like you this will be much difficult, I am especially interested in creating Database applications for which if someone can help to find step by step tutorial to create complete application using Oracle database ( i am doing job as oracle database developer - SQL and PLSQL ), if not MYSQL guide can be helpful.
Please share link(s) to get into it.

regards