INSERT INTO itemSalesPriceDetails (itemcode, UnitId, qty, rate, Incrate, itemid)
SELECT 
    i.itemcode,
    i.unit,
    1,
    i.rate,
    i.vatrate,
    i.id
FROM item i
WHERE i.itemcode NOT IN (
    SELECT itemcode 
    FROM itemSalesPriceDetails 
    WHERE itemcode IS NOT NULL
);