select

SELECT `old_id`
FROM `xls_about_us`
    UNION SELECT `old_id`   FROM
    `xls_bodies`
    UNION SELECT `old_id`   FROM
    `xls_capacity_building`
    UNION SELECT `old_id`   FROM
    `xls_climate_action`
    UNION SELECT `old_id`   FROM
    `xls_conferences`
    UNION SELECT `old_id`   FROM
    `xls_education_outreach`
    UNION SELECT `old_id`   FROM
    `xls_events`
    UNION SELECT `old_id`   FROM
    `xls_finance`
    UNION SELECT `old_id`   FROM
    `xls_french_events`
    UNION SELECT `old_id`   FROM
    `xls_gender`
    UNION SELECT `old_id`   FROM
    `xls_land_use`
    UNION SELECT `old_id`   FROM
    `xls_markets_nonmarkets`
    UNION SELECT `old_id`   FROM
    `xls_mitigation`
    UNION SELECT `old_id`   FROM
    `xls_paris_agreement`
    UNION SELECT `old_id`   FROM
    `xls_parties_nonparty_stakeh`
    UNION SELECT `old_id`   FROM
    `xls_resilience`
    UNION SELECT `old_id`   FROM
    `xls_science`
    UNION SELECT `old_id`   FROM
    `xls_the_convention`
    UNION SELECT `old_id`   FROM
    `xls_the_kyoto_protocol`
    UNION SELECT `old_id`   FROM
    `xls_transparency_reporting`