SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;

BEGIN TRANSACTION T2
    SELECT
        SUM(Cena)
    FROM
        Bilety
-- STEP 2 RUN ABOVE

    UPDATE Wycieczki
        SET cena = cena * 2
    WHERE
        kraj = 'Bangkok'
-- STEP 4 RUN BETWEEN 2 AND 4

COMMIT TRANSACTION T2