Use this.

select coalesce(a.id,b.id,c.id)id,
isnull(max(name),'')name,
isnull(max(address),'')address,
isnull(max(descri),'')descr from tablea a full join tableb b
on a.id=b.id
full join tablec c
on a.id=c.id
group by coalesce(a.id,b.id,c.id)