@Override
  public ColumnTransformer visitTimeStampOperand(
      TimestampOperand timestampOperand, ColumnTransformerVisitorContext context) {
    ColumnTransformer res =
        context.cache.computeIfAbsent(
            timestampOperand,
            e -> {
              TimeColumnTransformer timeColumnTransformer =
                  new TimeColumnTransformer(TypeFactory.getType(context.getType(timestampOperand)));
              context.leafList.add(timeColumnTransformer);
              return timeColumnTransformer;
            });
    res.addReferenceCount();
    return res;
  }
Responsible for constructing {@link ColumnTransformer} through Expression.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/visitor/ColumnTransformerVisitor.java