Du kan använda MERGE:
MERGE INTO PRD_DTLS A USING
(
SELECT
PRODUCT,
TXN_DATE,
LAG(NO_OF_TXNS) OVER(
PARTITION BY PRODUCT
ORDER BY
TXN_DATE
) AS PREV_TXN
FROM
PRD_DTLS
)
B ON ( A.PRODUCT = B.PRODUCT
AND A.TXN_DATE = B.TXN_DATE )
WHEN MATCHED THEN UPDATE SET A.PREV_DAY_TXN = CASE
WHEN B.PREV_TXN IS NOT NULL THEN B.PREV_TXN
ELSE 0
END;
Skål!!