Storing historical updates in a database

I strongly prefer to create a history table whose columns *exactly* match those of the original table (except that "identity" property is turned off; history table is kept in sync: if the original table gets modified, the history table gets the same mod).  As modifications are made, the entire old row is copied to the history table.  You don't need to copy the current row as it exists in the main table.

Scott, I assume you'd add some kind of audit columns as well right? Datetime stamp, user ID, etc?

You could.  Personally, I do that in a separate table.  I want to always be able to use the history table anywhere in code I use original table; and be able to do a SELECT * UNION SELECT * from the original table and its history.

Apologies if I did not explain the problem correctly.  I have a scheduled task that replaces the last progress update with the current one. So whenever there is a progress update a field would have to be created almost  dynamically. Is that advisable? Should I be storing all previous progress updates separated with a special character ?

Can you give some sample data, and an example of the update process? What's your input and what's your desired output? That will give us something more concrete to base our advise on.
Dynamic solutions usually are a last resort option though, as they're complex to build and maintain, and usually suboptimal when executed repeatedly. But we would only know for sure if we know what you're trying to achieve.

Here is an example. I have three fields in salesforce namely
Beneficiary Progress Update
FeedbackSent
LastProgress Update
I have a scheduled task that checks if the Beneficiary Progress Update has a value and the Feedback Sent is Pending. If it is it copies the Beneficiary Progress Update value  into the Last Progress Update value and updates the feedback sent to pending. So currently I am storing only two progress updates. I want to be able to store historical progress updates.
One other solution that came to my mind was when the scheduled task moves the progress updates to the LastProgress Updates store all previous progress update separated with a special character. Will that work ?

I think you need to move away from the idea of storing your progress update history in the same table as you are currently using. Create a new table, and insert the historical updates into this table in one of the ways described above.
So when your scheduled task finds len(beneficiary progress update) > 0 and FeedbackSent = 'Pending':

Insert last progress update into new table (e.g. ProgressUpdateHistory)
Update LastProgress Update with Beneficiary Progress Update
Update FeedbackSent to Sent

You probably would have to insert a few identifiers into your ProgressUpdateHistory table as well to identify what it belongs to (I'm sure there's still more data in the underlying table you're not mentioning).

when the scheduled task moves the progress updates to the LastProgress Updates store all previous progress update separated with a special character. Will that work ?

yes, that can work for numerical values or short (one word) strings. you would make the 'LastProgress' a varchar field and append each next history value to the previous string using a separator like space, comma or pipe symbol.

however, you should be aware of the limitations and shortcomings of that "method". a "history string" is a good visualization for a few values, but not for hundreds. even for 10 values you may have problems to show the whole contents of the field. you also can't add some meta information to the value (for example who had made the update and when) and you badly can search for old values. if any of these points might become a requirement, you should go the relational database way (as described by Koen) and have a second table which is linked by key to the original table and has a date or serial number which it could be ordered by. doing so, allows to show both original data and the history data like

key data history
-----------------------
abc  3      22
                 17
xyz  9       8
                 5
                 6
                 3

Select allOpen in new window

and easily add some more columns like date or responsible person.

Sara