Find the temp usage of sessions - oracle database script

SELECT b.tablespace,
       ROUND(((b.blocks*p.value)/1024/1024),2)||'M' AS temp_size,
       a.inst_id AS INSTANCE,
       a.sid||','||a.serial# AS sid_serial,  NVL(a.username, '(oracle)') AS username,  a.program,  a.status,  a.sql_id  FROM gv$session a,  gv$sort_usage b,  gv$parameter p  WHERE p.name = 'db_block_size'  AND a.saddr = b.session_addr  AND a.inst_id=b.inst_id  AND a.inst_id=p.inst_id  ORDER BY temp_size desc  /