Please help me in tuning the query....

Question

SELECT   /*+ LEADING (WCL_EXPO) */
         MAX (a.clm_id) clm, a.clm_nbr, b.expo_nbr, b.entps_covg_cd_id,
         'open' status, a.uw_cmpy_map_id, a.rt_st_id, a.src_sys_id, suit_nbr
    FROM wcl_clm a,
         wcl_expo b,
         (SELECT DISTINCT clm_fil_nbr, expo_nbr, suit_nbr
                     FROM wcl_suit
                    WHERE ((litg_opn_dtm BETWEEN TO_DATE ('12/31/2010',
                                                          'MM/DD/YYYY'
                                             AND TO_DATE ('12/30/2011',
                                                          'MM/DD/YYYY'
                          )) c,
         wrd_st st,
         wrd_src_sys s
   WHERE a.clm_nbr = b.clm_nbr
     AND st.st_id = a.rt_st_id
     AND b.src_sys_id = a.src_sys_id
     AND b.clm_nbr = c.clm_fil_nbr
     AND b.expo_nbr = c.expo_nbr
     AND a.lob_map_id IN (18, 19)
     AND a.src_sys_id IN (1, 3, 4, 12, 13)
     AND a.pol_nbr IS NOT NULL
     AND a.row_log_del_ind = 'N'
GROUP BY a.clm_nbr,
         b.entps_covg_cd_id,
         b.expo_nbr,
         a.uw_cmpy_map_id,
         a.rt_st_id,
         a.src_sys_id,
         suit_nbr

Answer 1

SELECT   /*+ LEADING (WCL_EXPO) */
         MAX (a.clm_id) clm, a.clm_nbr, b.expo_nbr, b.entps_covg_cd_id,
         'open' status, a.uw_cmpy_map_id, a.rt_st_id, a.src_sys_id, suit_nbr
    FROM wcl_clm a,
         wcl_expo b,
         (SELECT DISTINCT clm_fil_nbr, expo_nbr, suit_nbr
                     FROM wcl_suit
                    WHERE ((litg_opn_dtm BETWEEN TO_DATE ('12/31/2010',
                                                          'MM/DD/YYYY'
                                             AND TO_DATE ('12/30/2011',
                                                          'MM/DD/YYYY'
                          )) c
--         wrd_st st--,
----         wrd_src_sys s --not used any where
WHERE    a.clm_nbr = b.clm_nbr
--     AND st.st_id = a.rt_st_id
     AND b.src_sys_id = a.src_sys_id
     AND b.clm_nbr = c.clm_fil_nbr
     AND b.expo_nbr = c.expo_nbr
     AND a.lob_map_id IN (18, 19)
     AND a.src_sys_id IN (1, 3, 4, 12, 13)
     AND a.pol_nbr IS NOT NULL
     AND a.row_log_del_ind = 'N'
     AND EXISTS (SELECT 1
                   FROM wrd_st st
                  WHERE st.st_id = a.rt_st_id)
GROUP BY a.clm_nbr,
         b.entps_covg_cd_id,
         b.expo_nbr,
         a.uw_cmpy_map_id,
         a.rt_st_id,
         a.src_sys_id,
         suit_nbrregards,
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