@Override
  public Expression visitFunctionExpression(FunctionExpression functionExpression, C context) {
    List<Expression> reconstructedChildren = getReconstructedChildren(functionExpression, context);
    return reconstructFunctionExpression(functionExpression, reconstructedChildren);
  }
Collect result from child, then reconstruct. For example, two child each give me 1 result, I
should use them to reconstruct 1 new result to upper level.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/visitor/ReconstructVisitor.java