select case c.nickName when null then '<no nick name>' else c.nickName end
from Customer c

// This NULL checking is such a common case that most dbs
// define an abbreviated CASE form.  For example:
select nvl( c.nickName, '<no nick name>' )
from Customer c

// or:
select isnull( c.nickName, '<no nick name>' )
from Customer c

// the standard coalesce abbreviated form can be used
// to achieve the same result:
select coalesce( c.nickName, '<no nick name>' )
from Customer c
