Explain plan Takes a long time

[Subha]

SQL> EXPLAIN PLAN FOR SELECT vw.CASE_ID
2 FROM prod.DOC_PROD_CASE_VW VW
3 WHERE ( (VW.CASE_NO = '495796')
4 AND VW.CASE_ID in(551,593,552,801,799,761,550,
5 247,653,800,806,613,573,803,246,804,385,252,251,250,807,810,760,
6 770,715,101,244,794,656,253,673,755,100,767,553,217,243,219,245,
7 103,805,809,655,734,784,526,693,548,1,757,248,572,446,765,659,2,
8 756,808,758,802,0))
9 GROUP BY VW.CASE_ID
10 ORDER BY VW.CASE_ID;

Explained.

Elapsed: 00:00:42.06

if i remove the group by and order by .the explain plan completes in less than 3 seconds.

Otherwise
Explain plan takes a Long time.Some times the session itself freezes....

What can be done.