And there are two PROJECT,why…
The duplicate PROJECT in that list is a typo. Thank you for pointing it out. We’ve corrected it.
The PROJECT operator implements the SELECT that you write into your queries. So if you have:
SELECT name, date, id FROM your-dataset
… You’ll see an operator like this in the plan:
Project(name=[$0], date=[$1], id=[$2) ...
You can find more information about the relational algebra operator this is adapted from here.