tsql - T-SQL CASE Clause: How to specify WHEN NULL

Question

I wrote a T-SQL Statement similar like this (the original one looks different but I want to give an easy example here):

SELECT first_name + 
    CASE last_name WHEN null THEN 'Max' ELSE 'Peter' END AS Name
FROM dbo.person

This Statement does not have any syntax errors but the case-clause always chooses the ELSE-part - also if the last_name is null. But Why?

What I want to do is to unite first_name and last_name, but if last_name is null the whole name becomes null:

SELECT first_name +
   CASE last_name WHEN null THEN '' ELSE ' ' + last_name END AS Name 
FROM dbo.person

Do you know where the problem is?

Answer 1

CASE WHEN last_name IS NULL THEN '' ELSE ' '+last_name END