docs: public void generateOutputSchema(Database db)
      {
          // default behavior: just copy the input schema
          // to the output schema
          assert(m_children.size() == 1);
          AbstractPlanNode childNode = m_children.get(0);
          childNode.generateOutputSchema(db);
          // Replace the expressions in our children's columns with TVEs.  When
          // we resolve the indexes in these TVEs they will point back at the
          // correct input column, which we are assuming that the child node
          // has filled in with whatever expression was here before the replacement.
          // Output schemas defined using this standard algorithm
          // are just cached "fillers" that satisfy the legacy
          // resolveColumnIndexes/generateOutputSchema/getOutputSchema protocol
          // until it can be fixed up  -- see the FIXME comment on generateOutputSchema.
          m_hasSignificantOutputSchema = false;
          m_outputSchema = childNode.getOutputSchema().copyAndReplaceWithTVE();
      }