Multiple execution plan for the same sql_id

getHi,

Currently I am working on a performance issue with a quey whose performance get worse along the day maybe related with an inacurete stats. My scenario is:

Version:

SQL> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
PL/SQL Release 11.2.0.2.0 - Production
CORE    11.2.0.2.0      Production
TNS for Linux: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production

SQL:

SELECT *
FROM ESB_ATCOMRESTASK
WHERE 1=1
AND parent_batchNo IS NULL
AND NOT EXISTS
  (SELECT '1'
  FROM tr_upload up,
    esb_atComResTask tsk2
  WHERE up.batchNo       = tsk2.batchNo
  AND (tsk2.b atchNo     = esb_atComResTask.batchNo
  OR tsk2.parent_batchNo = esb_atComResTask.batchNo)