Timestamp Not Updating

[Mr Toner]

Got me a table with a field that should contain the date & time the record was inserted/updated:

CREATE TABLE `ae_users` (
  `location` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  `last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `item_name` tinytext COLLATE utf8_unicode_ci NOT NULL,
  `item_cost` decimal(10,0) NOT NULL,
  `item_percent` decimal(10,0) NOT NULL,
  PRIMARY KEY (`location`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

However, the value for last_updated is "0000-00-00 00:00:00" after this query is run:

$query = sprintf("INSERT INTO ae_users (location,last_update,item_name,item_cost,item_percent) 
   VALUES ('%s','%d','%s','%d','%d')
   ON DUPLICATE KEY UPDATE item_name=VALUES(item_name),item_cost=VALUES(item_cost),item_percent=VALUES(item_percent)",
   mysql_real_escape_string($listing, $dbh),
   time(),
   mysql_real_escape_string($item_name, $dbh),
   mysql_real_escape_string($item_cost, $dbh),
   mysql_real_escape_string($item_percent, $dbh)); 

Same result for insert or update. Server version is 5.1.52. Any suggestions why last_updated doesn't show the current timestamp?

[guelphdad]

drop last update from the insert entirely, it will still update.

[Mr Toner]

Ah, that's right. Seems having that there was causing (probably) an illegal value that was changed to "zero." Thanks for the second set of eyes! Congrats on 1500 posts, too!