When a domain name resolution request is initiated, a matched subdomain is first queried.
For example, suppose you have created one zone named example.com and added an A record set to it, with the Name field set to www, and you have also created another zone named www.example.com but have not added an A record set to this zone.
If a visitor accesses www.example.com, the domain name is first queried in the zone named www.example.com. However, no result will be returned because no record sets have been added to the zone.