newbie oracle błąd oświadczenie aktualizacja

oracle query:

UPDATE AIRMODEL_NETWORK_SUMMARY 
SET CASES_PRODUCED = (SELECT DISTINCT PRDCTN_RUN_ACTL_CASE_QTY
                       FROM AIRMODEL_NETWORK_SUMMARY, HISTORY_PRODUCTION, PERIOD_TO_PROCESS
                      WHERE AIRMODEL_NETWORK_SUMMARY.FSCL_WK_IN_YR_NUM = HISTORY_PRODUCTION.FSCL_WK_IN_YR_NUM 
                        AND AIRMODEL_NETWORK_SUMMARY.FSCL_YR_NUM = HISTORY_PRODUCTION.FSCL_YR_NUM 
                        AND AIRMODEL_NETWORK_SUMMARY.LOC_ID = HISTORY_PRODUCTION.LOC_ID 
                        AND HISTORY_PRODUCTION.FSCL_WK_IN_YR_NUM = PERIOD_TO_PROCESS.FSCL_WK_IN_YR_NUM 
                        AND HISTORY_PRODUCTION.FSCL_YR_NUM = PERIOD_TO_PROCESS.FSCL_YR_NUM);

zwraca następujący błąd:

ORA-01427: jednorzędowy Podzapytanie zwraca więcej niż jeden wiersz

Kolejna próba korekty:

 MERGE INTO AIRMODEL_NETWORK_SUMMARY AIRMODEL_NETWORK_SUMMARY1 
  USING (SELECT DISTINCT PRDCTN_RUN_ACTL_CASE_QTY, 
           AIRMODEL_NETWORK_SUMMARY2.rowid AS r 
      FROM AIRMODEL_NETWORK_SUMMARY AIRMODEL_NETWORK_SUMMARY2 
           INNER JOIN HISTORY_PRODUCTION 
              ON AIRMODEL_NETWORK_SUMMARY2.FSCL_WK_IN_YR_NUM = HISTORY_PRODUCTION.FSCL_WK_IN_YR_NUM 
                 AND AIRMODEL_NETWORK_SUMMARY2.FSCL_YR_NUM = HISTORY_PRODUCTION.FSCL_YR_NUM 
                 AND AIRMODEL_NETWORK_SUMMARY2.LOC_ID = HISTORY_PRODUCTION.LOC_ID 
           INNER JOIN PERIOD_TO_PROCESS 
              ON HISTORY_PRODUCTION.FSCL_WK_IN_YR_NUM = PERIOD_TO_PROCESS.FSCL_WK_IN_YR_NUM 
                 AND HISTORY_PRODUCTION.FSCL_YR_NUM = PERIOD_TO_PROCESS.FSCL_YR_NUM) 
   ON (AIRMODEL_NETWORK_SUMMARY1.rowid = r) 
 WHEN MATCHED THEN UPDATE 
  SET CASES_PRODUCED = PRDCTN_RUN_ACTL_CASE_QTY;

zwraca następujący błąd:

ORA-30926: nie można uzyskać stabilnego zestawu wierszy w tabelach źródłowych

Jestem noobem i potrzebują pomocy :(

Dziękuję Ci.