CodePaste.NET - Use PARSENAME to get the fully qualified object name

DECLARE @str nvarchar(128)
SET @str = '[AdventureWorks].[dbo].[ErrorLog]'
 
SELECT    ISNULL(PARSENAME(@str, 4), @@SERVERNAME) AS [ServerName],
        ISNULL(PARSENAME(@str, 3), DB_NAME()) AS [DatabaseName],
        ISNULL(PARSENAME(@str, 2), ISNULL([default_schema_name], 'dbo')) AS [SchemaName],
        PARSENAME(@str, 1) AS [ObjectName]
       
FROM [sys].[database_principals]
WHERE [name] = SYSTEM_USER