docs: public void resolveSortDirection() {
          AbstractPlanNode outerTable = m_children.get(0);
          if (m_joinType == JoinType.FULL) {
              // Disable the usual optimizations for ordering join output by
              // outer table only. In case of FULL join, the unmatched inner table tuples
              // get appended to the end of the join's output table thus invalidating
              // the outer table join order.
              m_sortDirection = SortDirectionType.INVALID;
              return;
          }
          if (outerTable instanceof IndexSortablePlanNode) {
              m_sortDirection = ((IndexSortablePlanNode)outerTable).indexUse().getSortOrderFromIndexScan();
          }
      }