Deleting All Non-Recently Updated Keys/Inserts MySQL - mysql

Question

I'm trying to create a DELETE statement in Java where after updating and inserting all new items into the DB, it deletes any old ones that were not affected by the update.
Reasoning: I'm hosting a game where items are saved upon logging out. Items are either updated or inserted depending on whether or not their reference exists. However, it is possible that a player could have dropped an item inside the game, thus no longer having ownership of it. I need to delete the reference to this item now that the player no longer has it.
tl;dr: Trying to write a DELETE FROM WHERE NOT IN for all non-updated objects belonging to the character
Table definition:
CREATE TABLE `inventoryitems` (
`inventoryitemid` int(10) unsigned NOT NULL AUTO_INCREMENT,
`type` tinyint(3) unsigned NOT NULL,
`characterid` int(11) DEFAULT NULL,
`accountid` int(11) DEFAULT NULL,
`itemid` int(11) NOT NULL DEFAULT '0',
`inventorytype` int(11) NOT NULL DEFAULT '0',
`position` int(11) NOT NULL DEFAULT '0',
`quantity` int(11) NOT NULL DEFAULT '0',
`owner` tinytext NOT NULL,
`petid` int(11) NOT NULL DEFAULT '-1',
`flag` int(11) NOT NULL,
`expiration` bigint(20) NOT NULL DEFAULT '-1',
`giftFrom` varchar(26) NOT NULL,
PRIMARY KEY (`inventoryitemid`),
KEY `CHARID` (`characterid`),
KEY `inventorytype` (`inventorytype`),
KEY `type` (`type`),
KEY `accountid` (`accountid`)
) ENGINE=InnoDB AUTO_INCREMENT=79597880 DEFAULT CHARSET=latin1