Does Llama Index have some sort of

class CustomSxQLRetriever(BaseRetriever):
    def _retrieve(self, query_bundle: QueryBundle) -> List[NodeWithScore]:
        """Retrieve nodes given query."""
        with self.callback_manager.as_trace("query"):
            with self.callback_manager.event(
                CBEventType.RETRIEVE,
                payload={EventPayload.QUERY_STR: query_bundle.query_str},
            ) as retrieve_event:
                retrieved_nodes, _ = self.retrieve_with_metadata(query_bundle)
                retrieve_event.on_end(
                    payload={EventPayload.NODES: retrieved_nodes},
                ) 
        return retrieved_nodes

engine = create_engine(CONN_STR)
sql_database = SQLDatabase(engine)
sql_retriever = CustomSQLRetriever(sql_database, return_raw=False)

class VeryCustomQueryEngine(CustomQueryEngine):
    """SQL Search but fallbacks to Vector Search Query Engine"""
    sql_retriever: CustomSQLRetriever
    vector_retriever: BaseRetriever
    response_synthesizer: BaseSynthesizer
    variable_data: Dict[str, Any]
    


    def custom_query(self, query_str: str):
        
        nodes = self.sql_retriever.retrieve(query)
        if len(nodes) > 0:
            print("GOT SQL RESPONSE SO PROCEED")
            response_obj = self.response_synthesizer.synthesize(query_str, nodes)
        return response_obj

synthesizer = get_response_synthesizer(response_mode="compact")
query_engine = VeryCustomQueryEngine(sql_retriever=sql_retriever, vector_retriever=vector_retriever, response_synthesizer=synthesizer, variable_data=variable_data, callback_manager=callback_manager)