Conditional Column Selections

[Doug]

I believe there is a way to make a conditional column selection on the SELECT statement but I am having difficultly finding succinct syntax.

Here is what I want to do:

I have 3 columns
FIRSTNAME
NICKNAME
LASTNAME

FIRSTNAME and LASTNAME are populated on every record. NICKNAME contains data only on occasion.

How can I make my SELECT statement do this:

concat(NICKNAME," ",LASTNAME) OR concat(FIRSTNAME," ",LASTNAME) ONLY WHEN NO NICKNAME OR NICKNAME IS NULL

Thank you for your help.