Final answer:
The SQL query calculates the total value of stock dividends adjusted for the exchange rate by joining two tables on a common national code.
Step-by-step explanation:
The result of the SQL query SELECT SUM(stock.stockdiv*nation.exchrate) FROM stock JOIN nation ON stock.natcode = nation.natcode is the total sum of the product of the stockdiv column from the stock table and the exchrate column from the nation table, for all rows where the natcode in both tables match. This is achieved through an SQL JOIN operation, which combines rows from multiple tables based on a related column between them. In this case, it calculates the total value of stock dividends adjusted for the nation's exchange rate.