1. A NOT IN condition referencing a subquery returning no rows returns all rows:
SELECT 'True' FROM employees WHERE department_id NOT IN (SELECT 0 FROM DUAL WHERE 1=2);2. Force sorting in a UNION to get Nth row:
select name_id "id", name_last "last", rownum "rownum" from name where name_seriesno = name_now(name_id) and (name_last, name_id) in ( select name_last, name_id from name where name_serisno = name_now(name_id) union select 'x', 'y' from dual where 1=2 ) group by name_id ,name_last ,rownum having rownum = 5; id last rownum ----- --------------- ---------- @133 O'Leary 5