Enrico, 1) EnumerableMergeJoinRule does not seem to work (see https://issues.apache.org/jira/browse/CALCITE-2592 ). It seems to be broken since Calcite 1.9.0
2) It turns out you need to add RelTraitDefs explicitly to the planner, otherwise it just ignores the traits (or something like that). Would you please try adding org.apache.calcite.rel.RelCollationTraitDef#INSTANCE to the list of traits you use for planning? (see https://github.com/diennea/herddb/blob/0c7c01584350d57d8102511b987e5f880f3f65bd/herddb-core/src/main/java/herddb/sql/CalcitePlanner.java#L412 ) PS. You are using a somewhat creative way of planning the whole thing as Enumerable then converting the plan relations to your own format. Vladimir
