Hi all, I'd like to bring to the attention of a more people a problem which has been there for long, ie, self joins. Currently, we have many troubles with them. This has been reported several times to the community and seems to affect many people, but as of now no solution has been accepted for it.
I created a PR some time ago in order to address the problem ( https://github.com/apache/spark/pull/21449), but Wenchen mentioned he tried to fix this problem too but so far no attempt was successful because there is no clear semantic ( https://github.com/apache/spark/pull/21449#issuecomment-393554552). So I'd like to propose to discuss here which is the best approach for tackling this issue, which I think would be great to fix for 3.0.0, so if we decide to introduce breaking changes in the design, we can do that. Thoughts on this? Thanks, Marco
