private Transformer getBuiltInScalarFunctionTransformer(
      FunctionExpression expression, IntermediateLayerVisitorContext context) {

    LayerReader childReader =
        this.process(expression.getExpressions().get(0), context).constructReader();
    return BuiltInScalarFunctionHelperFactory.createHelper(expression.getFunctionName())
        .getBuiltInScalarFunctionTransformer(expression, childReader);
  }
Responsible for constructing {@link IntermediateLayer} through Expression.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/visitor/IntermediateLayerVisitor.java