Always Have a Single, Authoritative Source For Your Schema
Everyone should know where the official schema resides, and have a frictionless experience in getting a fresh database setup. One should be able to walk up to a computer, get the latest from source control, build, and run a simple tool to setup the database (in many scenarios, the build process can even setup a database if none exists, so the process is one step shorter).
Always Version Your Database
The common goal is to propagate changes from development, to test, and ultimately to production in a controlled and consistent manner. A second goal is to have the ability to recreate a database at any point in time. This second goal is particularly important if you are shipping software to clients. If someone finds a bug in build 20100612.1 of your application, you must be able to recreate the application as it appeared in that build – database and all.