CREATE TABLE GSMDATA (
    ID          	INTEGER NOT NULL,
    ABONENTID     	INTEGER,
    XCOORD     	 	FLOAT,
    YCOORD      	FLOAT,
    TIMESESSION   	TIMESTAMP,
    CORRECTCOORDS 	SMALLINT
);

        SELECT
            AbonentId, MAX(TimeSession) as TimeSession
        FROM
            GsmData
        WHERE 
        	CorrectCoords = 1
        GROUP BY
            AbonentId

    FOR
        SELECT
            AbonentId, MAX(TimeSession) as TimeSession
        FROM
            GsmData
        WHERE 
        	CorrectCoords = 1
        GROUP BY
            AbonentId
        INTO
            :AbonentId,:TimeSession
    DO BEGIN
       SELECT
            Id,XCOORD,YCOORD
       FROM
           GsmData gd
       WHERE
       		(gd.TimeSession = :TimeSession) AND
       		(gd.AbonentId = :AbonentId)
       INTO
            :Id, :AbonentId, :TimeSession, :XCOORD, :YCOORD;
       SUSPEND;
    END

create view gsm_data_last as
select g1.* from gsmdata g1 
join (
   select ID, MAX(TimeSession) as TimeSession, AbonentId FROM GsmData GROUP BY AbonentId
) g2 on g1.ID = g2.ID  

   select ID, MAX(TimeSession) as TimeSession, AbonentId FROM GsmData GROUP BY AbonentId

Invalid expression in the select list (not contained in either an aggregate function or the GROUP BY clause)

SELECT COUNT(*) FROM ActualInfo

select g1.* from gsmdata g1 
join (
   select MAX(ID) as ID, AbonentId FROM GsmData GROUP BY AbonentId
) g2 on g1.Id = g2.Id