PL/SQL :: How To Create Special Column Which Represents Result Of A Query

I have a table MESSAGE which has some billion entries. The columns are msg_id, vehicle_id, timestamp, data, etc.I have another table VEHICLE which holds static vehicle data (about 20k rows) such as vehicle_id, licenceplate, etc.

My first target was to partition the table via timestamp (by range) and subpartition by vehicle_id (by hash).So I could easily drop old data by dropping old partitions and tablespaces.

Now comes the new difficult 2nd target: the messages of some vehicles must be kept forever.My idea is to add a column KEEP_DATA to the table MESSAGE. I could try to partition by timestamp AND KEEP_DATA, subpartion by vehicle_id.The problem of this idea is that i have to update billions of rows.

It would be perfect if there is a possibility to add this KEEP_DATA-flag to the table vehicle.Is there any way to "link" this information to a column in MESSAGE table?

I mean something like this:

alter table MESSAGE
add column (select keep_data from vehicle where VEHICLE.vehicle_id = MESSAGE.vehicle_id as keep_message) ;

Is there some possibility like that? Would the partitioning on this column / statement work?Would the value of the keep_message be calculated on runtime?

If so will the performance influence be noticeable?If so will the performance also sink if the application is querying all rows except the keep_message?