How to eleminate the co-releated Subquery to improve the query performance

Question

Please find the query below which takes long time to fetch the records.
SQL> SET LINE 120
SQL> EXPLAIN PLAN FOR select *
  2                 from KEMP_SRC a1
  3                 where ('MOFF' is null or eq_name = 'MOFF')
  4                       and
  5                         is_ad_hoc <> 1
  6                         and (pb_proc_id is null
  7                         or pb_proc_id in (select proc_id from KEMP_CONFIG where frequency_type <> -1)
  8                         )
  9                    and     KEMPUtility.DTTM(end_dt, end_tm) in      (select max(KEMPUtility.DTTM(end_dt, end_tm))
10                                from KEMP_SRC a2
11                                where a2.eq_name = a1.eq_name
12                                and (a2.pb_proc_id = a1.pb_proc_id or (a2.pb_proc_id is null and a1.pb_proc_id is null))
13                                and a2.is_ad_hoc <> -1 -- repeating case
14                                group by eq_name, pb_proc_id
15                                );
Explained.
SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY());
PLAN_TABLE_OUTPUT
Plan hash value: 2624956131
| Id  | Operation             | Name                      | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT      |                           |     1 |    96 | 69399   (3)| 00:13:53 |
|*  1 |  FILTER               |                           |       |       |            |          |
|*  2 |   TABLE ACCESS FULL   | KEMP_SRC                  |  2896 |   271K|   124   (2)| 00:00:02 |
|*  3 |   TABLE ACCESS FULL   | KEMP_CONFIG               |     1 |    26 |     2   (0)| 00:00:01 |
|*  4 |    FILTER             |                           |       |       |            |          |
|   5 |     HASH GROUP BY     |                           |     1 |    35 |   125   (3)| 00:00:02 |
PLAN_TABLE_OUTPUT
|*  6 |      TABLE ACCESS FULL| KEMP_SRC               |   364 | 12740 |   124   (2)| 00:00:02 |
Predicate Information (identified by operation id):
   1 - filter(("PB_PROC_ID" IS NULL OR  EXISTS (SELECT /*+ */ 0 FROM
              "KEMP_CONFIG" "KEMP_CONFIG" WHERE "PROC_ID"=:B1 AND
              "FREQUENCY_TYPE"<>(-1))) AND  EXISTS (SELECT /*+ */ 0 FROM "KEMP_SRC" "A2" WHERE
              "A2"."EQ_NAME"=:B2 AND ("A2"."PB_PROC_ID"=:B3 OR :B4 IS NULL AND "A2"."PB_PROC_ID" IS
              NULL) AND "A2"."IS_AD_HOC"<>(-1) GROUP BY "EQ_NAME","PB_PROC_ID" HAVING
PLAN_TABLE_OUTPUT
              "KEMPUtility"."DTTM"(:B5,:B6)=MAX("KEMPUtility"."DTTM"("END_DT","END_TM"))))
   2 - filter("EQ_NAME"='BILAN_MAZOUT_BFOE' AND "IS_AD_HOC"<>1)
   3 - filter("PROC_ID"=:B1 AND "FREQUENCY_TYPE"<>(-1))
   4 - filter("KEMPUtility"."DTTM"(:B1,:B2)=MAX("KEMPUtility"."DTTM"("END_DT","END_TM")))
   6 - filter("A2"."EQ_NAME"=:B1 AND ("A2"."PB_PROC_ID"=:B2 OR :B3 IS NULL AND
              "A2"."PB_PROC_ID" IS NULL) AND "A2"."IS_AD_HOC"<>(-1))
28 rows selected.

Answer 1

When i comment the reference to a1 in the subquery , then the cost drastically reduced .
select *
  2                 from KEMP_SRC a1
  3                 where ('MOFF' is null or eq_name = 'MOFF')
  4                       and
  5                         is_ad_hoc != 1
  6                         and (pb_proc_id is null
  7                         or pb_proc_id in (select proc_id from KEMP_CONFIG where frequency_type  -1)
  8                         )
  9                    and     KEMPUtility.DTTM(end_dt, end_tm) in      (select max(KEMPUtility.DTTM(end_dt, end_tm))
10                                from KEMP_SRC a2
11                                where
                                             -- a2.eq_name = a1.eq_name
12                            --    and (a2.pb_proc_id = a1.pb_proc_id or (a2.pb_proc_id is null and a1.pb_proc_id is null))
13                                --and
                                             a2.is_ad_hoc != -1 -- repeating case
14                                group by eq_name, pb_proc_id
15                                );
PLAN_TABLE_OUTPUT
Plan hash value: 3739658629
| Id  | Operation              | Name                      | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT       |                           |    78 |  8190 |   249   (3)| 00:00:03 |
|*  1 |  FILTER                |                           |       |       |            |          |
|*  2 |   HASH JOIN            |                           |   203 | 21315 |   249   (3)| 00:00:03 |
|   3 |    VIEW                | VW_NSO_1                  |     7 |    63 |   125   (3)| 00:00:02 |
|   4 |     HASH UNIQUE        |                           |     7 |   245 |   125   (3)| 00:00:02 |
|   5 |      HASH GROUP BY     |                           |     7 |   245 |   125   (3)| 00:00:02 |
PLAN_TABLE_OUTPUT
|*  6 |       TABLE ACCESS FULL| KEMP_SRC               |  2896 |    98K|   124   (2)| 00:00:02 |
|*  7 |    TABLE ACCESS FULL   | KEMP_SRC               |  2896 |   271K|   124   (2)| 00:00:02 |
|*  8 |   TABLE ACCESS FULL    | KEMP_CONFIG |     1 |    26 |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter("PB_PROC_ID" IS NULL OR  EXISTS (SELECT /*+ */ 0 FROM
              "KEMP_CONFIG" "KEMP_CONFIG" WHERE "PROC_ID"=:B1 AND
              "FREQUENCY_TYPE"<>(-1)))
PLAN_TABLE_OUTPUT
   2 - access("$nso_col_1"="KEMPUTILITY"."DTTM"("END_DT","END_TM"))
   6 - filter("A2"."EQ_NAME"='BILAN_MAZOUT_BFOE' AND "A2"."IS_AD_HOC"<>(-1))
   7 - filter("EQ_NAME"='BILAN_MAZOUT_BFOE' AND "IS_AD_HOC"<>1)
   8 - filter("PROC_ID"=:B1 AND "FREQUENCY_TYPE"<>(-1))