SELECT d.*,
ARRAY_DISTINCT(ARRAY {"name": v.country_name, "code":v.country_code} FOR v IN d.sellers END) AS countires
FROM default AS d
WHERE .....
OR
SELECT d.*,
(SELECT DISTINCT seller.country_name AS name, seller.country_code AS code
FROM d.sellers AS seller
) AS countries
FROM default AS d
WHERE .....
SELECT d.*,
(SELECT seller.country_name AS name, seller.country_code AS code, COUNT(1) AS counter
FROM d.sellers AS seller
GROUP BY seller.country_name , seller.country_code) AS countries
FROM default AS d
WHERE .....