How to get current instance name from T-SQL

How can I get the SQL Server server and instance name of the current connection, using a T-SQL script?

Just found the answer, in this SO question (literally, inside the question, not any answer):

SELECT @@servername

returns servername\instance as far as this is not the default instance

SELECT @@servicename

returns instance name, even if this is the default (MSSQLSERVER)

How about this:

EXECUTE xp_regread @rootkey='HKEY_LOCAL_MACHINE',
                   @key='SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQl',
                   @value_name='MSSQLSERVER'

This will get the instance name as well. null means default instance:

SELECT SERVERPROPERTY ('InstanceName')

http://technet.microsoft.com/en-us/library/ms174396.aspx

SELECT @@servername will give you data as server/instanceName

To get only the instanceName you should run select @@ServiceName query .

Why stop at just the instance name? You can inventory your SQL Server environment with following:

SELECT  
    SERVERPROPERTY('ServerName') AS ServerName,  
    SERVERPROPERTY('MachineName') AS MachineName,
    CASE 
        WHEN  SERVERPROPERTY('InstanceName') IS NULL THEN ''
        ELSE SERVERPROPERTY('InstanceName')
    END AS InstanceName,
    '' as Port, --need to update to strip from Servername. Note: Assumes Registered Server is named with Port
    SUBSTRING ( (SELECT @@VERSION),1, CHARINDEX('-',(SELECT @@VERSION))-1 ) as ProductName,
    SERVERPROPERTY('ProductVersion') AS ProductVersion,  
    SERVERPROPERTY('ProductLevel') AS ProductLevel,
    SERVERPROPERTY('ProductMajorVersion') AS ProductMajorVersion,
    SERVERPROPERTY('ProductMinorVersion') AS ProductMinorVersion,
    SERVERPROPERTY('ProductBuild') AS ProductBuild,
    SERVERPROPERTY('Edition') AS Edition,
    CASE SERVERPROPERTY('EngineEdition')
        WHEN 1 THEN 'PERSONAL'
        WHEN 2 THEN 'STANDARD'
        WHEN 3 THEN 'ENTERPRISE'
        WHEN 4 THEN 'EXPRESS'
        WHEN 5 THEN 'SQL DATABASE'
        WHEN 6 THEN 'SQL DATAWAREHOUSE'
    END AS EngineEdition,  
    CASE SERVERPROPERTY('IsHadrEnabled')
        WHEN 0 THEN 'The Always On Availability Groups feature is disabled'
        WHEN 1 THEN 'The Always On Availability Groups feature is enabled'
        ELSE 'Not applicable'
    END AS HadrEnabled,
    CASE SERVERPROPERTY('HadrManagerStatus')
        WHEN 0 THEN 'Not started, pending communication'
        WHEN 1 THEN 'Started and running'
        WHEN 2 THEN 'Not started and failed'
        ELSE 'Not applicable'
    END AS HadrManagerStatus,
    CASE SERVERPROPERTY('IsSingleUser') WHEN 0 THEN 'No' ELSE 'Yes' END AS InSingleUserMode,
    CASE SERVERPROPERTY('IsClustered')
        WHEN 1 THEN 'Clustered'
        WHEN 0 THEN 'Not Clustered'
        ELSE 'Not applicable'
    END AS IsClustered,
    '' as ServerEnvironment,
    '' as ServerStatus,
    '' as Comments

I found this:

EXECUTE xp_regread
        @rootkey = 'HKEY_LOCAL_MACHINE',
        @key = 'SOFTWARE\Microsoft\Microsoft SQL Server',
        @value_name = 'InstalledInstances'

That will give you list of all instances installed in your server.

The ServerName property of the SERVERPROPERTY function and @@SERVERNAME return similar information. The ServerName property provides the Windows server and instance name that together make up the unique server instance. @@SERVERNAME provides the currently configured local server name.

And Microsoft example for current server is:

SELECT CONVERT(sysname, SERVERPROPERTY('servername'));

This scenario is useful when there are multiple instances of SQL Server installed on a Windows server, and the client must open another connection to the same instance used by the current connection.