BUG: df.getitem returning copy instead of view for unique column in dup index
- [x] closes #45316
- [x] closes #41062
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

I think this is more intuitive (and "more" correct) than the previous behavior.
perf impact? > perf impact?

Good point. Let's check for uniqueness or that the key is unique, so we only have the drop duplicates call if we have non unique columns @phofl can you merge master and some comments Done This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Merged master again @phofl could you merge in one more time. Looks pretty good. Done thanks @phofl very nice as always