弃用数据库模式中的列的最佳方法是什么？

After reading through many of the questions here about DB schema migration and versions, I've come up with a scheme to safely update DB schema during our update process. The basic idea is that during an update, we export the database to file, drop and re-create all tables, and then re-import everything. Nothing too fancy or risky there.After reading through many of the questions her