Most 'alter column' sub-operations require that the table has a single column primary key or a unique, non-nullable column. This is required for backfilling.
'alter column' operations that have no sub-operations other than a rename should work on tables that don't meet this restriction because they don't require backfills.
Failed to start migration: migration is invalid: a backfill is required but table "products" doesn't have a single column primary key or a UNIQUE, NOT NULL column
Most 'alter column' sub-operations require that the table has a single column primary key or a unique, non-nullable column. This is required for backfilling.
'alter column' operations that have no sub-operations other than a rename should work on tables that don't meet this restriction because they don't require backfills.
This series of migrations should work:
but the second migration currently fails with: