Handling changes to facts

[lcm]

Hi All,

I have a question on how best to handle the scenario when something that has been recorded in a fact table changes at a later date. The situation is as follows:

• For an educational institution
  
• Fact table storing a student's graded results for a particular unit - 1 row per student/unit inserted when a grade is detected
  
• Occasionally an error will be discovered after a unit has been graded (eg. wrong grade entered) and this will then be corrected in the source system.

If I have already inserted a row into the fact table what is the best way to handle these subsequent changes?

Any help/suggestions greatly appreciated!

Thanks.
lcm

[ngalemmo]

You have two choices:

1. update in place

2. expire the old row and insert a new row

It all depends if you want an audit trail of the changes.

[lcm]

Thanks for the response - it confirms my suspicions.

And yes, in this case they want to see the various values so I'll go down the row expiration route.

Thanks again,
lcm

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