@Override
  public IntermediateLayer visitConstantOperand(
      ConstantOperand constantOperand, IntermediateLayerVisitorContext context) {
    if (!context.expressionIntermediateLayerMap.containsKey(constantOperand)) {
      try {
        IntermediateLayer intermediateLayer =
            new ConstantIntermediateLayer(
                constantOperand, context.queryId, context.memoryAssigner.assign());
        context.expressionIntermediateLayerMap.put(constantOperand, intermediateLayer);
      } catch (QueryProcessException e) {
        throw new RuntimeException(e);
      }
    }

    return context.expressionIntermediateLayerMap.get(constantOperand);
  }
Responsible for constructing {@link IntermediateLayer} through Expression.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/visitor/IntermediateLayerVisitor.java