All the schema delta files are checked into repository. They themselves can be version tracked. Different branches can have different versions of a delta file.

All the schema delta files are checked into repository. They themselves can be version tracked. Different branches can have different versions of a delta file. Merging branches need to merge the changes of the delta file. Might need special attention since merging sql statements needs special care. Edit: Or you might choose to be explicit with the version of the delta files in a branch. Each branch has its own delta file naming format. When merging into main, roll the changes from all delta files into a new main delta file. If main has moved forward a lot, you have to insert the changes carefully.