Ok, obviously I never done web development, but why you would want declare schema from rails? And ActiveRecord is some kind of ORM (the buzzword I was hearing lately, but never actually care to fully understand it)?

Now I am reading book High Performance MySQL: Optimization, Backups, and Replication (yes, I know this post about PostgreSQL) and there are so much stuff to know, so this ORM thing seems like a toy.

So what is wrong to creating schema with plain old (database specific) SQL?