Question

While designing a table which have impact based on date (e.g. Currency Rate) which one is better?

1. Effective date (Find out max(Effective date) and get the current value)
2. From Date – To Date condition (With greater than equals sysdate)

Rgrds.

Answer 1

It depends. You have a table representing changes to a particular entity, and you want to record when the entity changed, and when the change was replaced by a subsequent change.

1. If you record just the Effective Date for each event, INSERTs are simpler: they don’t need to find the earlier record to update it. However, querying becomes more complex – you’ll need to run a window over the dataset to find which record is applicable at any one time, potentially resulting in poorer performance.

Another downside is that this model is open-ended; you can’t record a currency as “permanently closed” (which you could do if you had an End date).

2. If you record the Start and End dates for each event, queries are simpler: you only need to look at each row individually to know whether it is “current” as of any point in time or not. INSERTs, however, are slightly more complex – when you insert a new event, you have to update the earlier event to mark its End date.

This model is closed-ended; you can put a End date on the final event and have no “open” record.