Sorry if I'm misunderstanding, but if the only thing you have is the "current state" SQL file, how do you make automated changes to the schema? The point of mig

Sorry if I'm misunderstanding, but if the only thing you have is the "current state" SQL file, how do you make automated changes to the schema? The point of migration tools is that making a change is simply a matter of making a new file that lays out that change, and then running the tool. Do you alter the DB manually?