PDOStatement::fetch causing 500 Internal server error [closed] - php

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I'm currently developing an auditing web app using PHP and MySQL. The app was developed locally using XAMPP without any issues. However after deploying it to my host's servers one of the php files that accesses the database using PDO started to generate a 500 internal server error. After some debugging the fetch() function was found to be the source.
// works
$sql="INSERT INTO subsection (section_id) VALUES (:section_id)";
$query=$db->prepare($sql);
$query->execute(array(':section_id'=>$section_id));
// doesn't work
$sql="SELECT audit_id FROM audit
WHERE audit_id < :audit_id
ORDER BY audit_id DESC LIMIT 1";
$query=$db->prepare($sql);
$query->execute(array(':audit_id'=>$audit_id));
$prevAuditId=$query->fetch()[0]; // <-- error generated here
phpinfo() reveals that the host's servers are running PHP version 5.33 and PDO support is enabled. So to summarise, the web app works locally on a XAMPP installation and when hosted PDO appears to function except for the fetch method().
Any clarification on this issue would be greatly appreciated.

Answer 1

The problem is that you're using PHP 5.3, but the array-dereferencing syntax you've used is only allowed from PHP 5.4 and up.
Here's your code:
$prevAuditId=$query->fetch()[0];
The problem is nothing to do with the PDO call, it's caused by the [0] at the end.
Getting an array element from a function call like this is called "dereferencing" the array. PHP 5.3 doesn't support this. If you need to stick with PHP 5.3, you'll have to split it out into two lines:
$auditRecord=$query->fetch();
$prevAuditId=$auditRecord[0];
Alternatively, you could upgrade your server to PHP 5.4 (or later), where your original syntax is valid.
Hope that helps.