@Override
  public IntermediateLayer visitCaseWhenThenExpression(
      CaseWhenThenExpression caseWhenThenExpression, IntermediateLayerVisitorContext context) {
    throw new UnsupportedOperationException("CASE expression cannot be used with non-mappable UDF");
  }
Responsible for constructing {@link IntermediateLayer} through Expression.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/visitor/IntermediateLayerVisitor.java