How about:

SELECT Rooms.iNoRoom;
   FROM Rooms;
   WHERE Rooms.iNoRoom NOT EXIST IN;
      (SELECT Reservations.iNoRo;
          FROM Reservations;
          WHERE (ldStart BETWEEN dStart AND dEnd) OR;
          (ldEnd BETWEEN dStart AND dEnd))

Where ldStart and ldEnd are the start and end date of the reservation you are trying to make.

HTH

>ROOMS :
>inoroom (Integer, 6, Primary Key)
>ctype (Character, 15)
>
>RESERVATIONS :
>iid (Integer,6,primary key)
>inoro (Integer,6)
>dstart (Start date)
>dend (End date)
>
>inoroom field is related 1-m with inoro into RESERVATIONS table....
>
>The problem is that I want to see all rooms that are NOT reserved between 2 variables date... Some of these rooms are not present in RESERVATIONS table and some are present betwwen these 2 dates and some on other dates... A room, of course can be reserved during different periodes.... Like a hotel reservation....