@Override public RelNode visit(LogicalJoin join) { // to the best of my knowledge join.systemFieldList is always empty Preconditions.checkState(join.getSystemFieldList().isEmpty(), "join.systemFieldList is not empty!"); final RelNode left = join.getLeft().accept(this); final RelNode right = join.getRight().accept(this); return new LogicalJoin( cluster, copyOf(join.getTraitSet()), left, right, copyOf(join.getCondition()), join.getVariablesSet(), join.getJoinType(), join.isSemiJoinDone(), ImmutableList.<RelDataTypeField>of() ); }