Julian>I don’t know how this is possible. It may be a bug. I did spent noticeable amount of time debugging traits, and I did try my best at summarizing the issue in the very first mail of the thread. The very first email is enough. It is truly sad you don'
The description follows after "My analysis is as follows" (please, I beg you read it) In a couple of words: the collation for LogicalProject comes from the source logical plan (it is computed based on multi-collated values). And multi-collated values is placed to "don't care" subset at the very start of the planning since Volcano ALWAYS erases composite traits. That is why I suggest we remove RelTraitSet#simplify and allow RelSubsets to have composite traits. It would still follow "quality-of-service" logic you describe, and it won't result in LogicalProject(subset=[rel#11:Subset#1.NONE.[0]], input=rel#9:Subset#0.NONE.[], Y=[$1]) conditions. Vladimir
