para os powerdns definem como padrão um registro com nome vazio
nano /etc/pdns/pdns.conf
gmysql-any-query=select COALESCE(b.content,c.content,d.content,e.content,f.content) content, \
COALESCE(b.ttl,c.ttl,d.ttl,e.ttl,f.ttl) ttl, \
COALESCE(b.prio,c.prio,d.prio,e.prio,f.prio) prio, \
COALESCE(b.type,c.type,d.type,e.type,f.type) type, \
COALESCE(b.domain_id,c.domain_id,d.domain_id,e.domain_id,f.domain_id) domain_id, \
a.mydomain name \
from \
(select '%s' mydomain) a \
left outer join records b on b.name = SUBSTRING_INDEX(a.mydomain, '.', -4) and b.type = 'A' \
left outer join records c on c.name = SUBSTRING_INDEX(a.mydomain, '.', -3) and c.type = 'A' \
left outer join records d on d.name = SUBSTRING_INDEX(a.mydomain, '.', -2) and d.type = 'A' \
left outer join records e on e.name = SUBSTRING_INDEX(a.mydomain, '.', -1) and e.type = 'A' \
left outer join records f on f.name = SUBSTRING_INDEX(a.mydomain, '.', 0) and f.type = 'A' \
limit 1;