List<Items> items = new List<Items>();
items.add(new Item(1,1,2));
items.add(new Item(2,2,2));
items.add(new Item(3,3,3));
items.add(new Item(1,2,3));

List<ItemInDB> itemsInDB = new List<ItemInDB>();

for(Item aItem : items){

    itemsInDB.add ([
        Select Id, Name
        from ItemInDB
        where ItemInDB.property1 =: aItem.prop1
        and ItemInDB.property2 =: aItem.prop2
        and ItemInDB.property3 =: aItem.prop3 ] );
}