@Override
  public List<PartialPath> visitUnaryExpression(
      UnaryViewExpression unaryViewExpression, Void context) {
    ViewExpression expression = unaryViewExpression.getExpression();
    return this.process(expression, null);
  }
Use this visitor to find all the paths of time series used in one expression.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/view/visitor/GetSourcePathsVisitor.java