langchain/memory/chat_message_histories/sql.py/SQLChatMessageHistory/__init__
class SQLChatMessageHistory:    def __init__(
        self,
        session_id: str,
        connection_string: str,
        table_name: str = "message_store",
    ):
        self.table_name = table_name
        self.connection_string = connection_string
        self.engine = create_engine(connection_string, echo=False)
        self._create_table_if_not_exists()

        self.session_id = session_id
        self.Session = sessionmaker(self.engine)