Any pgroll operations[0] that require a change to an existing column, such as adding a constraint, will create a new copy of the column and backfill it using 'up' SQL defined in the migration and apply the change to that new column.
There are no operations that will modify the data of an existing column in-place, as this would violate the invariant that the old schema must remain usable alongside the new one.
There are no operations that will modify the data of an existing column in-place, as this would violate the invariant that the old schema must remain usable alongside the new one.
[0] - https://github.com/xataio/pgroll/tree/main/docs#operations-r...