Why @@SERVERNAME Returns NULL?

The @@SERVERNAME can return NULL, when you accidentally delete the server. Most probably by this query

sp_dropserver '<ServerName>'

After the SQL Server restart, the @@SERVERNAME started returning NULL. You can confirm this; if the following query returns no records, the local server was deleted.

Select * From sys.servers Where server_id=0

Solution 1

Run the following query to add the server back.

sp_addserver '<ServerName>',local

Solution 2

I would recommend you to use

Select ServerProperty('ServerName')

This approach returns the machine name, even if the sever name is not present in the sys.servers table.