MySQL-如何检查START TRANSACTION是否处于活动状态

问题描述：

我注意到START TRANSACTION自动COMMIT先前的查询.因此，在整个事务结束之前我已经调用了多个存储过程，因此我需要检查我是否在START TRANSACTION内部.阅读手册后，我了解到START TRANSACTION内的autocommit设置为false，但看起来不是这样.我编写了以下过程:

I have noticed that START TRANSACTION automatically COMMIT the previous queries. Because of this and the fact that I have several stored procedure called before the end of the whole transaction, I need to check if I am inside a START TRANSACTION or not. Reading the manual I understood that autocommit is set to false inside a START TRANSACTION, but it doesn't seem like this. I have written the following procedure:

    CREATE DEFINER=`root`@`localhost` PROCEDURE `test_transaction`()
BEGIN

show session variables like 'autocommit';

start transaction;

show session variables like 'autocommit';

COMMIT;

show session variables like 'autocommit';

END

但是每个show session variables like 'autocommit';都显示autocommit = ON，而我希望第二个显示为autocommit = OFF.

But each show session variables like 'autocommit'; show autocommit=ON while I expected the second to be autocommit=OFF.

如何检查我是否在START TRANSACTION内?

我需要执行此检查，因为我的procedure1需要START TRANSACTION，然后它调用也需要START TRANSACTION的procedure2.但是，让我们假设我有第三个过程different_procedure，它也需要调用procedure2，但是在这种情况下，different_procedure不使用START TRANSACTION.在这种情况下，我需要procedure2来检查是否启动了START TRANSACTION.我希望这足够清楚.

I need to perform this check because I have procedure1 that need START TRANSACTION then it calls procedure2 that also need START TRANSACTION. But let's suppose I have a third procedure different_procedure that also need to call procedure2 but in this case different_procedure doesn't use START TRANSACTION. In this scenario I need procedure2 to check if START TRANSACTION was initiated. I hope this is enough clear.

答

您可以创建一个函数，该函数将利用仅在事务内发生的错误:

You can create a function that will exploit an error which can only occur within a transaction:

DELIMITER //
CREATE FUNCTION `is_in_transaction`() RETURNS int(11)
BEGIN
    DECLARE oldIsolation TEXT DEFAULT @@TX_ISOLATION;
    DECLARE EXIT HANDLER FOR 1568 BEGIN
        -- error 1568 will only be thrown within a transaction
        RETURN 1;
    END;
    -- will throw an error if we are within a transaction
    SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
    -- no error was thrown - we are not within a transaction
    SET TX_ISOLATION = oldIsolation;
    RETURN 0;
END//
DELIMITER ;

测试功能:

set @within_transaction := null;
set @out_of_transaction := null;

begin;
    set @within_transaction := is_in_transaction();
commit;

set @out_of_transaction := is_in_transaction();

select @within_transaction, @out_of_transaction;

结果:

@within_transaction | @out_of_transaction
--------------------|--------------------
                  1 |                   0

通过MariaDB，您可以使用@@in_transaction

With MariaDB you can use @@in_transaction

MySQL-如何检查START TRANSACTION是否处于活动状态

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