SQL SERVER – Discussion – Effect of Missing Identity on System – Real World Scenario

About a week ago, SQL Server Expert, Imran Mohammed, provided a script, which will list all the missing identity values of a table in a database. In this post, I asked my readers if any could write a similar or better script. The results were interesting. While no one provided a new script, my question sparked a very active discussion that is still ongoing.

When providing the script, Imran asked me if I knew of any specific circumstances in which this kind of query could be useful, as he could not think of an instance where it would be necessary to find a missing identity. I was unable to think of a single reason for listing missing identities in a table. I posted Imran’s script on the assumption that someone would come up with an improved script, but as mentioned earlier, nobody did. Instead, we have been able to follow a very interesting discussion on subject of the need, if any, for listing Missing Identity values.

So, the question is this: “Do you know a real-world scenario where a Missing Identity value in any table can create problems?“

I have already received some extremely interesting comments from many experts, and all have posed the above question in one form or another. At this moment, I am still trying to think of an example from my own experience, but have yet to find one. Imran has since come up with one good example. Here is what he and other experts have suggested so far.

Jacob Sebastian – IDENTITY values are not expected to be sequential and there are all chances of having missing identity values, the most common cause is transaction rollbacks.

Simon Worth – The identity column is basically just a random number – even though they come sequentially. A developer making an assumption that the next record inserted will have an identity that is 1 more than the last inserted record. And if this is the case – then there are flaws in the logic of the developer.

Jacob Sebastian – What if the value in my table is 1, 2, 3, 5, 6 etc where “4″ is missing from the sequence. So what is the importance of knowing whether a table has missing identity values or not?

Imran Mohammed – If you use Identity property as your most unique column and Transaction Identifier, then definitely you would want to know why few transaction did not completely, Is there any specific fashion these transaction fails (Can be found out looking at missing values of identity)… Could be helpful to debug.

Now it is your turn. Let us have your thoughts.

Reference : Pinal Dave (http://blog.sqlauthority.com)