Sketch based join optimisation

[hmottestad]

GitHub issue resolved: #

Briefly describe the changes proposed in this PR:

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PR Author Checklist (see the contributor guidelines for more details):

• my pull request is self-contained
• I've added tests for the changes I made
• I've applied code formatting (you can use mvn process-resources to format from the command line)
• I've squashed my commits where necessary
• every commit message starts with the issue number (GH-xxxx) followed by a meaningful description of the change

[kenwenzel]

@hmottestad Looks really cool 🚀

[hmottestad]

Thanks. It's been on my mind for a few months now and finally I've managed to build a prototype.