Query returns no results if an id value is selected

I have the following table:

CREATE TABLE IF NOT EXISTS `inventory` (
 `id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
 `products_id` INT(11) UNSIGNED DEFAULT NULL,
 `options_id` INT(11) UNSIGNED DEFAULT NULL,
 `options_values_id` INT(11) UNSIGNED DEFAULT NULL,
 `sku` VARCHAR(255) NOT NULL,
 PRIMARY KEY (`id`),
 UNIQUE KEY `products` (`products_id`,`options_id`,`options_values_id`),
 UNIQUE KEY `sku` (`sku`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1;

I'm running the following insert on it:

INSERT INTO inventory (
   products_id,
   options_id,
   options_values_id,
   sku
) VALUES (
   2,
   4,
   5,
   'K12R-1687'
);

After running this, I can execute mysql_insert_id($db->link) and get the new auto-increment ID. However, if I run the following query right after that within Zen Cart 1.5, I get no results ($result->RecordCount() equals zero):

$result = $db->Execute("SELECT id FROM inventory WHERE sku = 'K12R-1687' LIMIT 1");

If I then copy this query and run it through PHPMyAdmin, I get the id value expected.

If I change the query to this, then it returns the results:

$result = $db->Execute("SELECT id, sku FROM inventory WHERE sku = 'K12R-1687' LIMIT 1");

Of if I change it to this, it finds the products_id but is missing the id naturally:

$result = $db->Execute("SELECT products_id FROM inventory WHERE sku = 'K12R-1687' LIMIT 1");

No queries which get only the id work.

What the heck is going on here?

In your SELECT query, have you tried wrapping id in backticks? ie: id

Might also suggest looking at a related thread: https://www.zen-cart.com/showthread.php?214560-Query-Issue

Solution offered is around bottom of page 2 or top of page 3.

Adding the backticks fixed the issue.