LEFT JOIN DEFAULT NULL VALUE

I had query simplified like this :

SELECT a.id, a.name, b.* FROM a LEFT JOIN b ON a.id=b.id

Which b is from group concat select (very dynamic column). Sometime there are 3 column in b, sometime 10 column depend on filtering.

What i want is something like this :

SELECT a.id, a.name, IFNULL(b.*) FROM a LEFT JOIN b ON a.id=b.id

I already look here and here and the answer is always repeating per column. But i can't apply ifnull per columns because i didn't know what the column is. There are any other aproach for replacing null values from left join ?