Vervang null-waarden in sql met behulp van de select-instructie in mysql?

Je hebt veel opties om NULL-waarden in MySQL te vervangen:

CASE

select case 
    when fieldname is null then '123' 
    else fieldname end as fieldname 
from tablename 

COALESCE

select coalesce(fieldname, '123') as fieldname 
from tablename 

IFNULL

select ifnull(fieldname, '123') as fieldname 
from tablename