docs: public void addAggregate(ExpressionType aggType,
                               boolean isDistinct,
                               Integer aggOutputColumn,
                               AbstractExpression aggInputExpr)
      {
          m_aggregateTypes.add(aggType);
          if (isDistinct)
          {
              m_aggregateDistinct.add(1);
          }
          else
          {
              m_aggregateDistinct.add(0);
          }
          m_aggregateOutputColumns.add(aggOutputColumn);
          if (aggType.isNullary()) {
              assert(aggInputExpr == null);
              m_aggregateExpressions.add(null);
          } else {
              assert(aggInputExpr != null);
              m_aggregateExpressions.add(aggInputExpr.clone());
          }
      }