insert into accs (id, money) values (1, 0);

update accs set money = money - 100 where id = 1;
update accs set money = money + 100 where id = 2;

start transaction

commit

rollback

start transaction;
    if ((select money from accs where id = 1) <= 100)
        rollback;
    end if;
    update accs set money = money - 100 where id = 1;
    update accs set money = money + 100 where id = 2;
commit;

• Записи целиком
• Отдельные поля

if v_1 + v_2 ≥ Δ then
   v_1 = v_1 − Δ
end if

if v_1 + v_2 ≥ Δ then
   v_2 = v_2 − Δ
end if

start transaction [режим] [изоляция] [настройки]

read {only | write}

[isolation level уровень]

commit [work] [and [no] chain]

rollback [work] [and [no] chain]

savepoint имя

rollback to savepoint имя

release savepoint имя

add constraint ... режим

• Не рекомендуется

set constraints {all|имена} {deferred|immediate}

• Проверка при deferred → immediate