where to get object_id value when issuing an item in Lineage2?

There was a need to issue items (things, adena, etc.) in the game Lineage2. The question arose: in the base of the game server (server in java ) there is a table items in which all items (things, resources, money, etc.) that players have are recorded. The value in the object_id column, as I understand it, is a unique thing id , which should be equal to the maximum object_id+1 for a new thing. The problem is that at one moment in the game a lot of these object_id can be generated and not all of them go to the items table. And even if you look at the items table and knock out a piece of a game monster, for example, when a rollout comes out, it has one оbject_id (and is in another table - itemsonground ), after you itemsonground up another object_id , and even when you quickly pick up and I'm alone on the server, then the object_id lifted item is not equal to the object_id-1 knocked out. And maybe on +30 , +59 , etc. differ. And if you do not assign this object_id , then you can issue the thing only once, after that, when you execute the next sql query, an exception arises that object_id have primary key..... in general, this is not the case anymore. If you had a similar experience, write how you did it.