No it isn't? Forward migration: add date column, set = date(day, month, year) for existing records, drop is valid date constraint, drop day/month/year columns

No it isn't? Forward migration: add date column, set = date(day, month, year) for existing records, drop is valid date constraint, drop day/month/year columns Down migration: add day/month/year columns, add is valid date constraint, set day/month/year = appropriate datepart of date, drop date column for trivial example.