/media/sda-magnetic/david/Dok-15-2023-11-27/fernuni-hagen/cs-i-ii/old-cs-2-02/http-2022-05-11/sql001.txt

SELECT DISTINCT * FROM (SELECT x FROM a UNION SELECT x FROM b)x ORDER BY x;
SELECT DISTINCT * FROM (SELECT x FROM a INTERSECT SELECT x FROM b)x ORDER BY x;


SELECT DISTINCT x FROM ((SELECT DISTINCT x FROM (SELECT x FROM a UNION SELECT x FROM b)x ORDER BY x) INTERSECT SELECT x FROM c)x ORDER by x;


SELECT DISTINCT * FROM 
(
    SELECT DISTINCT x FROM (SELECT x FROM a INTERSECT SELECT x FROM c)x 
    UNION 
    SELECT DISTINCT x FROM (SELECT x FROM b INTERSECT SELECT x FROM c)x 
)x ORDER BY x;