I'm trying to figure out what would be the best way to have a history on a database, to track any Insert/Delete/Update that is done. The history data will need to be coded into the front-end since it will be used by the users. Creating "history tables" (a copy of each table used to store history) is not a good way to do this, since the data is spread across multiple tables.My Answer
At this point in time, my best idea is to create a few History tables, which the tables would reflect the output I want to show to the users. Whenever a change is made to specific tables, I would update this history table with the data as well.
I'm trying to figure out what the best way to go about would be. Any suggestions will be appreciated.
I am using Oracle + VB.NET
Personally, I would stay away from triggers. They can be a nightmare when it comes to debugging and not necessarily the best if you are looking to scale out.The first answer was the suggestion of a history table along with a trigger. I wanted to dive into it a little further here.
If you are using an PL/SQL API to do the INSERT/UPDATE/DELETEs you could manage this in a simple shift in design without the need (up front) for history tables.
All you need are 2 extra columns, DATE_FROM and DATE_THRU. When a record is INSERTed, the DATE_THRU is left NULL. If that record is UPDATEd or DELETEd, just "end date" the record by making DATE_THRU the current date/time (SYSDATE). Showing the history is as simple as selecting from the table, the one record where DATE_THRU is NULL will be your current or active record.
Now if you expect a high volume of changes, writing off the old record to a history table would be preferable, but I still wouldn't manage it with triggers, I'd do it with the API.
I don't particularly care for triggers as they can "hide" actions from you. But the answer IS valid, it's the easy way to go in my opinion.
As stated above, I prefer one table, with the DATE_FROM (or create date) and the DATE_THRU. DATE_THRU is null until that record has been changed in some way. If the record has been updated, the old one will get a DATE_THRU of the current date/time and a new record will be INSERTed. If DELETEd, just the UPDATE of DATE_THRU will be performed.
I tend to think of addresses when thinking of something like this. An address is created on day 1. On day 2, the person comes back and changes their zip code. There are now 2 records in the table associatied with that customer and only one that is active (Day 2's).
Like I said in my answer though, if this is a high volume table with lots of changes to be expected, you may have to rethink this (I still wouldn't go with the trigger approach). Either keep my method and have a retention policy for records that have been end dated (DATE_THRU NOT NULL) and write them off somewhere else or go with the history table, but write the records via the PL/SQL API.
You also have to ask yourself if you really need to keep track of changes. Does it really matter? Can this be handled in the design another way? Can it be handled by not letting certain records be UPDATEd or DELETEd?