DELETE
FROM
    eds_conference
WHERE
    conf_uri IN (
        SELECT
            conf_uri
        FROM
            (
                SELECT
                    conf_uri
                FROM
                    eds_conference
                GROUP BY
                    conf_uri
                HAVING
                    count(conf_uri) > 1
            ) a
    )
AND id NOT IN (
    SELECT
        MIN(id)
    FROM
        (
            SELECT
                MIN(id) AS id
            FROM
                eds_conference
            GROUP BY
                conf_uri
            HAVING
                count(conf_uri) > 1
        ) b
);