Sometimes it is critical to ensure a group of queries are all executed successfully to maintain the integrity of our data. Let's say we have a banking app where we need to subtract funds from one account and add funds to another:

$mysqli->query ("UPDATE 'accounts' SET 'balance' = 'balance'-1000000 WHERE 'user' = 'Bob'");
$mysqli->query ("UPDATE 'accounts' SET 'balance' = 'balance'+1000000 WHERE 'user' = 'Fred'");

What if one of the queries fails? To mitigate the chances of misplacing our millions due to some possible error we must ensure that both queries are executed with the expected result before committing any changes to the data. This where transactions are useful. We can run the queries, then check if some conditions are met before committing the changes in the data:

UPDATE `mytable` SET `myColumn` = TRIM(CHAR(9) FROM TRIM(`myColumn`));

UPDATE  `table_to_update` a
        INNER JOIN `table_to_read` b
            ON a.`CountryName` COLLATE utf8_general_ci LIKE b.`CountryName` COLLATE utf8_general_ci
SET     a.`ccTLD` = b.`ccTLD` 

• Microsoft SQL Server 2008 R2
• Microsoft SQL Server 2012

• MySQL Database v5.0.45
• MySQL Workbench v6.0.8.11354 build 833