MySQL : transaction within a stored procedure

Question

The basic structure of my stored procedure is,

BEGIN

    .. Declare statements ..

    START TRANSACTION;

        .. Query 1 ..
        .. Query 2 ..
        .. Query 3 ..

    COMMIT;

END

MySQL version: 5.1.61-0ubuntu0.11.10.1-log

Currently, if 'query 2' fails, result of 'query 1' is committed.

• How can I rollback the transaction if any of the query fails?

Answer 1

Take a look at http://dev.mysql.com/doc/refman/5.0/en/declare-handler.html

Basically you declare error handler which will call rollback

START TRANSACTION;

DECLARE EXIT HANDLER FOR SQLEXCEPTION 
    BEGIN
        ROLLBACK;
        EXIT PROCEDURE;
    END;
COMMIT;

Answer 2

Just an alternative to the code by rkosegi,

BEGIN

    .. Declare statements ..

    DECLARE EXIT HANDLER FOR SQLEXCEPTION 
    BEGIN
          .. set any flags etc  eg. SET @flag = 0; ..
          ROLLBACK;
    END;

    START TRANSACTION;

        .. Query 1 ..
        .. Query 2 ..
        .. Query 3 ..

    COMMIT;
    .. eg. SET @flag = 1; ..

END

Answer 3

Here's an example of a transaction that will rollback on error and return the error code.

DELIMITER $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `SP_CREATE_SERVER_USER`(
    IN P_server_id VARCHAR(100),
    IN P_db_user_pw_creds VARCHAR(32),
    IN p_premium_status_name VARCHAR(100),
    IN P_premium_status_limit INT,
    IN P_user_tag VARCHAR(255),
    IN P_first_name VARCHAR(50),
    IN P_last_name VARCHAR(50)
)
BEGIN

    DECLARE errno INT;
    DECLARE EXIT HANDLER FOR SQLEXCEPTION
    BEGIN
    GET CURRENT DIAGNOSTICS CONDITION 1 errno = MYSQL_ERRNO;
    SELECT errno AS MYSQL_ERROR;
    ROLLBACK;
    END;

    START TRANSACTION;

    INSERT INTO server_users(server_id, db_user_pw_creds, premium_status_name, premium_status_limit)
    VALUES(P_server_id, P_db_user_pw_creds, P_premium_status_name, P_premium_status_limit);

    INSERT INTO client_users(user_id, server_id, user_tag, first_name, last_name, lat, lng)
    VALUES(P_server_id, P_server_id, P_user_tag, P_first_name, P_last_name, 0, 0);

    COMMIT WORK;

END$$
DELIMITER ;

This is assuming that autocommit is set to 0. Hope this helps.

Answer 4

[ This is just an explanation not addressed in other answers ]

At least in recent versions of MySQL, your first query is not committed .

If you query it under the same session you will see the changes, but if you query it from a different session, the changes are not there, they are not committed .

What's going on?

When you open a transaction, and a query inside it fails, the transaction keeps open, it does not commit nor rollback the changes.

So BE CAREFUL , any table/row that was locked with a previous query like SELECT ... FOR SHARE/UPDATE , UPDATE , INSERT or any other locking-query, keeps locked until that session is killed (and executes a rollback), or until a subsequent query commits it explicitly ( COMMIT ) or implicitly , thus making the partial changes permanent (which might happen hours later, while the transaction was in a waiting state).

That's why the solution involves declaring handlers to immediately ROLLBACK when an error happens.

---

Extra

Inside the handler you can also re-raise the error using RESIGNAL , otherwise the stored procedure executes "Successfully" :

BEGIN
    DECLARE EXIT HANDLER FOR SQLEXCEPTION 
        BEGIN
            ROLLBACK;
            RESIGNAL;
        END;

    START TRANSACTION;
        #.. Query 1 ..
        #.. Query 2 ..
        #.. Query 3 ..
    COMMIT;
END