На Oracle:
select a.*
from FILMS as a
where exists (select 1
from WATCHED as b
where ','||b.ids_films||',' like '%,'||to_char(a.id)||',%' and b.id_user = 1);
FILMS - таблица всех фильмов (id, name)
WATCHED - таблица просмотров типа: id_user = 1, ids_films = '1,2,3' (id фильмов через запятую)