T-SQL: Investigating session activity

Shows what is currently running on an instance including SQL text.

SELECT 
DB_NAME(req.database_id) as [Database],
sqltext.TEXT,
req.session_id,
s.login_time,
req.status,
req.command,
req.cpu_time,
req.total_elapsed_time,
s.login_name, s.last_request_start_time,
req.reads, req.writes
FROM sys.dm_exec_requests req
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS sqltext
left join sys.dm_exec_sessions s on s.session_id = req.session_id
inner join sys.databases d on d.database_id = req.database_id
where req.session_id > 50

Shows details of all connected sessions on an instance, can be narrowed down by uncommenting login_name

SELECT
session_id, login_time, host_name, program_name, cpu_time, client_interface_name, 
login_name, [status], last_request_start_time, last_request_end_time 
FROM sys.dm_exec_sessions s
--where login_name = 'sa'
ORDER BY login_time DESC