@Override
  public String toString() {
    return functionName
        + argumentTypes.stream().map(Type::toString).collect(joining(", ", "(", "):"))
        + returnType;
  }
The absolute canonical name of the function.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/function/BoundSignature.java