Select Statement

From: KK (anonymous_at_discussions.microsoft.com)
Date: 05/11/04 

Date: Tue, 11 May 2004 10:12:36 -0700

This is regarding a SQL Select statement
I have a table with 3 columns First Name, Last Name ,
CompanyName
I want a result of companyName, using a select statement
with the condition that
if CompanyName is Null then result should have LastName +
FirstName

something like
if CompanyName is null Then
Select LastName + FirstName from Table
else
Select CompanyName from Table

Can this if..else be used in a single Select statement?