im not sure i understand exactly what you're saying but lemee put this idea up and tell me if it's close to what you're doing.
diablo 2 and ever quest both have this method of game play, where if a user has bought or picked up an item, it not only goes into his inventory but posts somewhere so that uniqly he's the only one with those items. so, in essence, if your user picks up an item, place it into a table called, say, inventory and make another table called inventoryItems or whatever. in table inventory store values like this:
Player | InventoryItemsID
FrozNic | 12, 43, 35, 32, 822
comma delemted...
or another way to make this table would be, if you have only a certain amount of items that a player can have, make that many columns and once the columns are filled, the player can't have anymore items...
so it would look like this:
Player | item1 | item2 | item3 | etc
FrozNic | 12 | 43 | 35 | 32 | 822 | etc
in inventoryItems, store values like this:
ID | item
12 | shortsword
and any other details you want with it (abilities for that item (etc))
does that makes sense? i'm not sure if that's your problem but if it is, that should work just fine.