@Override
  public void bindInputLayerColumnIndexWithExpression(
      Map<String, List<InputLocation>> inputLocations) {
    for (Expression expression : expressions) {
      expression.bindInputLayerColumnIndexWithExpression(inputLocations);
    }

    final String digest = getExpressionString();
    if (inputLocations.containsKey(digest)) {
      inputColumnIndex = inputLocations.get(digest).get(0).getValueColumnIndex();
    }
  }
example: select udf(a, b, udf(c)) from root.sg.d;

<p>3 expressions [root.sg.d.a, root.sg.d.b, udf(root.sg.d.c)] will be in this field.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/multi/FunctionExpression.java