Using NOT EXISTS() is a lot better than NOT IN(). The latter, as defined by the SQL standard, has confusing behaviour with NULLs. x NOT IN(y1, y2) is defined to

Using NOT EXISTS() is a lot better than NOT IN(). The latter, as defined by the SQL standard, has confusing behaviour with NULLs. x NOT IN(y1, y2) is defined to expand to x <> y1 AND x <> y2. If any of these are NULL, the whole expression is NULL. Which means no rows match. Fun, ain't it?