Testing a ROW expression with IS NULL only reports TRUE if every single column is NULL. Нужно об этом знать, чтобы на напороться на ошибки в своём коде.
SELECT
(NULL, NULL) IS NULL as "(NULL, NULL) IS NULL", --true
(NULL, NULL) IS NOT NULL as "(NULL, NULL) IS NOT NULL", --false
NOT (NULL, NULL) IS NULL as "NOT (NULL, NULL) IS NULL", --false
(1, NULL) IS NULL as "(1, NULL) IS NULL", --false
(1, NULL) IS NOT NULL as "(1, NULL) IS NOT NULL", --false --!!!
NOT (1, NULL) IS NULL as "NOT (1, NULL) IS NULL" --true --!!!@sqlhub