Domain Context

-- Current server login
select system_user;

-- Current database user
select user_name();

-- List all sysadmin members
SELECT r.name AS role,m.name AS member FROM sys.server_principals r JOIN sys.server_role_members rm ON r.principal_id=rm.role_principal_id JOIN sys.server_principals m ON rm.member_principal_id=m.principal_id WHERE r.name='sysadmin';

-- Default domain of the SQL Server
select default_domain();

-- Hex SID for a given Windows account
select sys.fn_varbintohexstr(SUSER_SID('{domain}\\Administrator'));