Asif,

If it is your first article then I must say -decently written article.

I have also dealt with such situations many times but what I noticed in your solution was that you did not handle the case if maximum possible Invoice Id (i.e. yy-99999) was already generated. However, you put enough attention not to let generate a duplicate.

Anyways, it was a good article and keep sharing.

[Aarez]