Why does NVL always evaluate 2nd parameter

Question

Does anyone know, why Oracle\'s NVL (and NVL2) function always evaluate the second parameter, even if the first parameter is not NULL?

Answer 1

Here is a post where Tom Kyte confirms that decode and case short circuit but not nvl but he doesn't give justification or documentation for why. Just states it to be:

http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:926029357278#14932880517348

So in your case you should use decode or case instead of nvl if an expensive function will be called in your query.