@task(tags=["extract"])
    def extract_mail_domain() -> pd.DataFrame:
        db = Db.Db("mydb")
        db.init_sqlalchemy(slave=True)

        sql_query = """
            SELECT
                id as mail_domain_id,
                domain as label,
                email_domain_group_id as mail_domain_group_id
            FROM email_domain ed
            LEFT JOIN email_domain_group_has_domain edghd ON (ed.id = edghd.email_domain_id)
        """

        dataframe = pd.read_sql_query(sql_query, db.get_engine(),)
        db.close()

        if len(dataframe) > 0:
            return dataframe

        raise prefect.engine.signals.SKIP()