SELECT Contentgroup, count(distinct Album, Contentgroup) as pocet_alb
FROM
(
    SELECT Contentgroup, Album FROM `zahranicni`
    UNION ALL
    SELECT Contentgroup, Album FROM `domaci`      
) s
group by ContentgroupSELECT Contentgroup, count(distinct Album, Contentgroup) as pocet_alb
FROM
(
    SELECT Contentgroup, Album FROM `zahranicni`
    UNION ALL
    SELECT Contentgroup, Album FROM `domaci`      
) s
group by Contentgroup