Rollback multiple update query if one fails - php

Question

So what I am doing is am having multiple UPDATE queries, which changes the group name in the tbl_groups table and then updates all the users in tbl_users which belongs to that group, but if the user update query fails, it updates group, but I want to update both together or none, am using PHP and MySQL.

Answer 1

It sounds like all you need to do is use transactions.
You must use InnoDB tables to use transactions (actually, some other DB engines have transactions, but InnoDB is most common with MySQL).
Issue the "BEGIN TRANSACTION" query before the first update.
If any query fails, issue the "ROLLBACK" query to undo everything.
It's really pretty simple.
And if you ever decide you want to do a partial rollback (back to some point after the beginning of the transaction), then you can use "ROLLBACK TO SAVEPOINT savepoint_name". You will have had to issue the "SAVEPOINT savepoint_name" query 1st.
E.g., in PHP
mysql_query("BEGIN TRANSACTION");
$result1 = mysql_query("UPDATE `tbl_groups` SET `user_id` = 5 WHERE `group_id` = 3");
if($result1 === false) {
mysql_query("ROLLBACK");
}
mysql_query("SAVEPOINT savepoint1");
$result2 = mysql_query("UPDATE `tbl_users` SET `group_id` = 3 WHERE `user_id` = 5");
if($result === false) {
ROLLBACK TO SAVEPOINT savepoint1;
}
// COMMIT saves the changes to the db, making them visible to other sessions
// if the ROLLBACK TO SAVEPOINT statement executed, then only changes up to that SAVEPOINT will be saved
// if no ROLLBACK statements were executed, then all changes will be saved (assuming no MySQL errors that cause implicit ROLLBACK)
mysql_query('COMMIT');

Answer 2

use transactions with the best isolation level
i prefer "repeatable read"( you cannot view others data and vise verse until you committed the transaction ) is always good and it is default for innodb storage engine
if you are not using innodb then change the isolation level with
SET GLOBAL tx_isolation='REPEATABLE-READ'; or
SET SESSION tx_isolation='REPEATABLE-READ';
the rest of details are given by #Buttle Butkus

Answer 3

Set the relation between tbl_groups and tbl_users to ON DELETE CASCADE. Then just update tbl_groups and the changes will cascade to related records in tbl_users. If you have to update your parent keys like this very often then you could maybe think about using a surrogate key instead.

Answer 4

Following example is based on object oriented style, make sure your Required database table Type is InnoDB as it supports transaction statement
Here i just want delete multiple record based on ids
$this->link_id->autocommit(FALSE);
// This above statement start the transaction by disabling auto commit where link_id refers to your MySQLi database connection
for($i=1; $i<=5; $i++){
$tSql = "DELETE FROM your_table"
. " WHERE id=" . $i;
$rs = $this->link_id->query($tSql);// execute the query
if($this->link_id->affected_rows == -1) // check if it fails
{
$_SESSION["error"] = "Sorry ! cant be deleted ! ";
$this->link_id->rollback(); // rollback the transaction
break; // break the loop
}
}
//check if there is some error or not, if no error then commit the transaction
if(empty($_SESSION["error"])){
$this->link_id->commit();
}