SQL query - Getting rows for values greater by 3 numbers or letters : Am trying to come up with a query where in i can return back values which has greater letters by 2 or 3 than the chosen letter.

For Example:

I have two columns which has letters **Column A** and **Column B**. I want to get back when **column B** is greater than **Column A** by two letters. 

Another Example. If a row in **Column A** is letter 'D' then it should get values only if row in **column B** 'F' because its greater by two letters.

Thanks in advance