Top 5 Resources to Become a Database Expert

I am a Cisco network engineer before. Later on, I decided to change my path to software field. Luckily, I got a slot of a Software Engineer in a Japanese owned Production company. The environment is quite different, though I have a very basic background in OOP and database. Now, my task is more on backend which is facing a lot of database scripts. By the way we are using an old school Power Builder for the front end. What would you recommend to further enhance my database skill? Help would be greatly appreciated.