A Sql To Get Sid Of Blocking Session

There are many sql to get this information. They are all good. I just share mine.

SELECT blocking_sid, num_blocked  FROM ( SELECT blocking_sid, SUM(num_blocked) num_blocked
    FROM ( SELECT l.id1, l.id2,  MAX(DECODE(l.block, 1, i.instance_name||'-'||l.sid,    2, i.instance_name||'-'||l.sid, 0 )) blocking_sid,
   SUM(DECODE(l.request, 0, 0, 1 )) num_blocked
   FROM gv$lock l, gv$instance i
  WHERE ( l.block!= 0 OR l.request > 0 ) AND
   l.inst_id = i.inst_id
  GROUP BY l.id1, l.id2)
GROUP BY blocking_sid
   ORDER BY num_blocked DESC)  WHERE num_blocked != 0 ;