MySQL database transaction, using the WordPress database object $wpdb. Requires the InnoDB table format.

wpdb-transactions

<?php
global $wpdb;
 
// Start Transaction
$wpdb->query( "START TRANSACTION" );
 
// Do some expensive/related queries here
//$wpdb->query("DELETE FROM table WHERE form_id = '1' ");
//$wpdb->query("DELETE FROM data WHERE form_id = '1' ");
// set $error variable value in error handling after $wpdb modifications
 
if ($error) {
    // Error occured, don't save any changes
    $wpdb->query( "ROLLBACK" );
} else {
   // All ok, save the changes
   $wpdb->query( "COMMIT" );
}
 
?>

You don't need this check if ($error) {. The $wpdb->query( "COMMIT" ); will automatically calls ROLLBACK in case some command inside the transactions will fail.

So code can be:

<?php
global $wpdb;
 
// Start Transaction
$wpdb->query( "START TRANSACTION" );
 
// Do some expensive/related queries here
//$wpdb->query("DELETE FROM table WHERE form_id = '1' ");
//$wpdb->query("DELETE FROM data WHERE form_id = '1' ");
// set $error variable value in error handling after $wpdb modifications
 
$wpdb->query( "COMMIT" );
?>