Blocked sessions

SELECT r.session_id AS blocked_session,
       r.blocking_session_id AS blocking_session,
       r.wait_type,
       r.wait_time / 1000 AS wait_seconds,
       s.login_name,
       s.program_name,
       LEFT(t.text, 200) AS blocked_query
FROM sys.dm_exec_requests r
JOIN sys.dm_exec_sessions s ON s.session_id = r.session_id
CROSS APPLY sys.dm_exec_sql_text(r.sql_handle) t
WHERE r.blocking_session_id <> 0
ORDER BY r.wait_time DESC