CREATE TABLE JOURNALFLY (
    JOURNALID      INTEGER PRIMARY KEY ,
    DATEARRIVAL    TIMESTAMP,
    DATEDEPARTURE  TIMESTAMP,
    FLYAREAID      INTEGER 
);
 
CREATE TABLE FlyArea (
       FlyAreaID            INTEGER PRIMARY KEY,
       SizeArea             VARCHAR(10)
);

CREATE EXCEPTION ErrorFlyArea 'Данная посадочная площадка уже занята';

CREATE OR ALTER TRIGGER FreeFlyArea FOR JournalFly
ACTIVE AFTER INSERT OR UPDATE
AS
DECLARE LFlyAreaID PKFIELD;
BEGIN 
FOR SELECT FlyAreaID FROM JournalFly WHERE NEW.DateArrival>=DateArrival AND NEW.DateArrival<=DateDeparture
INTO :LFlyAreaID
DO
BEGIN
 IF (NEW.FlyAreaID = LFlyAreaID)
  THEN EXCEPTION ErrorFlyArea;
  END
END