Apache Iceberg: insert into/merge into/insert overwrite VS MOR/COW

Question

i am learning iceberg currently. I can understand MOR and COW.

In MOR, delete files are created to track updates/deletes. In COW, old data files are copied into new data files and deletes/updates are written into the new data files.

but I have some questions:

• how MOR/COW relate to insert into/merge into/insert overwrite?

• how insert into/merge into/insert overwrite works under MOR and COW? I guess merge into only works with COW? Am I right?

• BTW, Why identifier fields cannot enforce uniqueness when insert into?