public PhysicalOperator getPhysicalOperator(PhysicalPlanCreator creator) throws IOException {
Prel child = (Prel) this.getChild();
PhysicalOperator childPOP = child.getPhysicalOperator(creator);
Sort g = new ExternalSort(childPOP, PrelUtil.getOrdering(this.collation, getChild().getRowType()), false);
return creator.addMetadata(this, g);
}