mysql transaction - roll back on any exception

Question

Is it possible to roll back automatically if any error occurs on a list of mysql commands?

for example something along the lines of:

begin transaction;

insert into myTable values1 ...
insert into myTable values2 ...;  -- will throw an error

commit;

now, on execute i want the whole transaction to fail, and therefore i should NOT see values1 in myTable. but unfortunately the table is being pupulated with values1 even though the transaction has errors.

any ideas how i make it to roll back? (again, on any error)?

EDIT - changed from DDL to standard SQL

Solution 1

You can use 13.6.7.2. DECLARE ... HANDLER Syntax in the following way:

DELIMITER $$

CREATE PROCEDURE `sp_fail`()
BEGIN
    DECLARE `_rollback` BOOL DEFAULT 0;
    DECLARE CONTINUE HANDLER FOR SQLEXCEPTION SET `_rollback` = 1;
    START TRANSACTION;
    INSERT INTO `tablea` (`date`) VALUES (NOW());
    INSERT INTO `tableb` (`date`) VALUES (NOW());
    INSERT INTO `tablec` (`date`) VALUES (NOW()); -- FAIL
    IF `_rollback` THEN
        ROLLBACK;
    ELSE
        COMMIT;
    END IF;
END$$

DELIMITER ;

For a complete example, check the following SQL Fiddle.

Solution 2

You could use EXIT HANDLER if you for example need to SIGNAL a specific SQL EXCEPTION in your code. For instance:

DELIMITER $$

CREATE PROCEDURE `sp_fail`()
BEGIN
    DECLARE EXIT HANDLER FOR SQLEXCEPTION
    BEGIN
        ROLLBACK;  -- rollback any changes made in the transaction
        RESIGNAL;  -- raise again the sql exception to the caller
    END;

    START TRANSACTION;
    insert into myTable values1 ...
    IF fail_condition_meet THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Custom error detected.', MYSQL_ERRNO = 2000;
    END IF;
    insert into myTable values2 ...  -- this will not be executed
    COMMIT; -- this will not be executed
END$$

DELIMITER ;

Solution 3

The above solution are good but to make it even simpler

DELIMITER $$

CREATE PROCEDURE `sp_fail`()
BEGIN
    DECLARE EXIT HANDLER FOR SQLEXCEPTION
    BEGIN
        ROLLBACK;  -- rollback any error in the transaction
    END;

    START TRANSACTION;
    insert into myTable values1 ...
    insert into myTable values2 ...  -- Fails
    COMMIT; -- this will not be executed
END$$

DELIMITER ;

Comments

[Alma Do]

This is pointless since transactions in MySQL do not support DDL

[Urbanleg]

thanks for the comment, i edited my original post

[wchiquito]

Have you considered using Handlers? 13.6.7.2. DECLARE ... HANDLER Syntax

[MDaniyal]

my question is, Is this stored procedure is going to be persisted in database forever?.

[RnMss]

@MDaniyal Short answer: Yes.

[MDaniyal]

Thanks for the answer :) .Do you think it is a good idea that we save a new stored procedure for every new script? as we have 10 to 15 scripts per release so we would have hundreds of stored procedures.

[Xenos]

If the exception occurs in the 1st INSERT, wouldn't MySQL do the 2nd and 3rd ones, leading sometimes to unexpected results?

[cdhowie]

@Xenos No, though time will be wasted. If either of the first two queries fails, _rollback is still set to 1 and so the function will execute ROLLBACK; instead of COMMIT;. However, the following queries will still execute (within the transaction) only to be ultimately rolled back later. It really baffles me that MySQL chose this continue-on-error behavior. Contrast this to PostgreSQL, which places the transaction in a failed state, guarantees all future queries in the transaction will fail (except ROLLBACK TO) and will implicitly rollback on commit.

[Malus Jan]

I wrote it ,but not working: the second line should generate an error because ID =1 exists in DB DELIMITER $$ CREATE PROCEDURE prod() BEGIN DECLARE _rollback BOOL DEFAULT 0; DECLARE CONTINUE HANDLER FOR SQLEXCEPTION SET _rollback = 1; START TRANSACTION; INSERT INTO table1 values (2, 'B'); INSERT INTO table1 values (1, 'A'); IF _rollback THEN ROLLBACK; ELSE COMMIT; END IF; END$$ DELIMITER ; CALL prod(); DROP PROCEDURE IF EXISTS prod;

[wchiquito]

@MalusJan: Can you give more information?. In the dbfiddle everything works as expected.

[Malus Jan]

@wchiquito I created a temporary table in mysql (table1) with 2 fields (id --> pk, name), I insert (1, 'Text') to database and after that I ran the above query. But it inserts (2, 'B').

[Malus Jan]

@wchiquito I found the problem. The table engine should be InnoDB

[Curtis]

Im using 5.2. RESIGNAL seems to have been added in 5.5. Any suggestions for how I can get the error message using 5.2?

[0x49D1]

In case you need to log the exception: ROLLBACK will reset all the exception details, so you should set some session variables BEFORE ROLLBACK and pass them to the logging procedure AFTER ROLLBACK and before RESIGNAL for example: gist.github.com/0x49D1/bbc73d9d59aafd16ced01e145c3b34b0

[joedotnot]

@anyone is this method / syntax only possible inside a stored proc ? how would you write transaction commit / rollback within a script only, to be executed by a client (say, HeidiSQL or Workbench) ?

[Prateek Pande]

Why using CONTINUE HANDLER for exception ? Why not EXIT HANDLER ?

[aSystemOverload]

This didn't work for me, it raised an error and issued a ROLLBACK, but for some reason didn't actually roll the transaction back.

[Enissay]

How to do the same without persisting the stored procedure in DB ? without even using SP, is it possible ?