[prodigal_erik]

In practice, you're writing code that has to deal with records that were updated by versions 3, 5, and 7 of your code but not 4 or 6. After a few years you can be sure somebody got it wrong at some point, and now you have records in a few out of the 2^n states where not even the developers can anticipate the system's behavior. The fix is to make ALTER incremental and less painful, not to stop writing down and checking your schema.

[jeltz]

And both MySQL and PostgreSQL have put in work to make ALTER less painful by reducing the situations where a full table rewrite is necessary. In PostgreSQL you can both add and remove columns without the table being rewritten as long as you do not set a default value. You can also increase the lengths of varchars without any rewrite.