docs: private boolean doesExpressionReallyMeanIn(VoltXMLElement expr) throws HSQLParseException {
          if (!expr.name.equals("operation")) {
              return false;
          }
          if (!expr.attributes.containsKey("optype") ||
              !expr.attributes.get("optype").equals("equal")) {
              return false;
          }
  
          // see if the children are "row" and "table" or "tablesubquery".
          int rowCount = 0;
          int tableCount = 0;
          int valueCount = 0;
          for (VoltXMLElement child : expr.children) {
              if (child.name.equals("row")) {
                  rowCount++;
              }
              else if (child.name.equals("table")) {
                  tableCount++;
              }
              else if (child.name.equals("value")) {
                  valueCount++;
              }
          }
          //  T.C     IN (SELECT ...) => row       equal                  tablesubquery => IN
          //  T.C     =  (SELECT ...) => columnref equal                  tablesubquery
          //  (C1,C2)  IN (SELECT ...) => row       equal/anyqunatified    tablesubquery
          //  (C1, C2) =  (SELECT ...) => row       equal                  tablesubquery
          if ((tableCount + rowCount > 0) && (tableCount + valueCount > 0)) {
              assert rowCount == 1;
              assert tableCount + valueCount == 1;
              return true;
          }
  
          return false;
      }