There are a few ways that I know to find the server’s domain name using a SQL script. I listed them below:

First: You can read the registry

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DECLARE @domain_name varchar(128), @key varchar(128);

SET @key = 'SYSTEM\ControlSet001\Services\Tcpip\Parameters\';
EXEC master..xp_regread @rootkey='HKEY_LOCAL_MACHINE', @key=@key,@value_name='Domain',@value=@domain_name OUTPUT;
SELECT 'Server Name: '+@@servername + ' Domain Name:'+convert(varchar(100),@domain_name)
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Another way is to issue this SQL command:

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SELECT DEFAULT_DOMAIN()
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In SQL Server 2000 you can run the following SQL script:

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EXEC master.dbo.xp_logininfo 'Default Domain' 
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