Table Scope problem in subquery

Question

I am trying to execute following update query:
UPDATE STG DAST     
     SET TRAVEL_COUNTRY = (SELECT TRAVEL_COUNTRY_FULL
FROM (SELECT TRAVEL_COUNTRY_FULL,
RANK() OVER(PARTITION BY A.PERSON_ID ORDER BY A.LAST_UPDATE_DATE DESC, A.LOC_START_DATE DESC, A.LOC_END_DATE ASC) RANK
FROM APPS.TCS_MIS_EIT_LOCATION_EX A
WHERE A.PERSON_ID = DAST.PERSON_ID
AND A.TRAVEL_TYPE = 'S'
AND '01-Nov-2011' BETWEEN A.EFFECTIVE_START_DATE AND A.EFFECTIVE_END_DATE
AND '01-Nov-2011' BETWEEN A.LOC_START_DATE AND A.LOC_END_DATE )
WHERE RANK = 1);
This is giving error as "*DAST.PERSON_ID* : invalid identifier".
But PERSON_ID is a column in STG table. As far as I know table in the outer subquery will be visible in the howsoever inner subquery. But here there seems some problems. Kindly help me solve this .

Answer 1

UPDATE  STG DAST
   SET  TRAVEL_COUNTRY = (
                          SELECT  MAX(TRAVEL_COUNTRY_FULL) KEEP(DENSE_RANK FIRST ORDER BY A.LAST_UPDATE_DATE DESC,A.LOC_START_DATE DESC,A.LOC_END_DATE ASC)
                            FROM  APPS.TCS_MIS_EIT_LOCATION_EX A
                            WHERE A.PERSON_ID = DAST.PERSON_ID
                              AND A.TRAVEL_TYPE = 'S'
                              AND DATE '2011-11-01' BETWEEN A.EFFECTIVE_START_DATE AND A.EFFECTIVE_END_DATE
                              AND DATE '2011-11-01' BETWEEN A.LOC_START_DATE AND A.LOC_END_DATE
                         );SY.