select t.* from tbname t,
(select station_id,min(station_date) mdate from tbname group by station_id) tt
where t.station_id=tt.station_id and t.station_date=tt.mdate;
(select station_id,min(station_date) mdate from tbname group by station_id) tt
where t.station_id=tt.station_id and t.station_date=tt.mdate;
WHERE EXISTS
(
SELECT 1
FROM (SELECT STATION_ID,MIN(STATION_DATE) MIN_DATE FROM T GROUP BY STATION_ID) B
WHERE A.STATION_ID=B.STATION_ID AND A.STATION_DATE=B.MIN_DATE
);