(select count(sid) from v$session where blocking_session = dbs.sid) sessions_blocked,
dbs.sql_id holding_sql_id, dbs.wait_class holding_class, dbs.event holding_event, dbs.seconds_in_wait holding_secs,
dws.sid waiting_sid, dws.serial# waiting_serial#, dws.username waiting_user, dws.sql_id waiting_sql_id, dws.wait_class waiting_class, dws.event waiting_event, dws.seconds_in_wait waiting_secs
from v$session dbs, v$session dws
where dws.blocking_session = dbs.sid
order by dbs.sid, dws.seconds_in_wait desc
/