Need an aplhanumeric auto incremtal field

[Arun_Mozhi]

I need to create a alphanumeric auto Incremental field. When a new issue is created, the values should automatically incremented. i.e. for first issue the value should be "abc1001". for Second issues the value should be "abc1002".

The incremental values should be specific to projects. i.e.  when the user creates an issue in project1, the value should be "ade1001" and when the user creates a new issue for project2, the value should be "abc1001"

The alphanumeric part will be derived based on two other fields from the issue. I'm trying to write a code in post function to populate alphanumeric values.