Filter(NULL IS NOT NULL) in Explain Plan ??

Question

Hi All,
Can someone please explain what this explain plan statement means? I see a filter(NULL IS NOT NULL) as the first statement - could not figure out why it came up so from googling.
My Query Used:
EXPLAIN PLAN FOR
MERGE INTO summary_bysrccd
USING
(SELECT LAST_DAY(TRUNC(to_timestamp(os.requestdatetime, 'yyyymmddhh24:mi:ss.ff4'))) AS SUMMARY_DATE,
os.acctnum,
ol.sourcecode AS sourcecode,
ol.sourcename AS sourcename,
count(1) cnt_articleview
FROM article_views os , master_sourcecode ol
where os.sourcecode = ol.sourcecode
AND os.acctnum IS NOT NULL
AND ol.sourcecode IS NOT NULL
AND os.requestdatetime IS NOT NULL
AND UPPER(os.success_ind) = 'S'
     AND (
          ('INCR'  = 'FULL'
          AND  (get_date_timestamp(os.requestdatetime) BETWEEN TO_DATE('23-AUG-2011 00:00:00','DD-MON-YYYY HH24:MI:SS') AND TO_DATE('27-AUG-2011 23:59:59','DD-MON-YYYY HH24:MI:SS')
          AND   os.entry_CreatedDate BETWEEN TO_DATE('22-AUG-2011 00:00:00','DD-MON-YYYY HH24:MI:SS') AND TO_DATE('28-AUG-2011 00:00:00','DD-MON-YYYY HH24:MI:SS')
          OR ('INCR' = 'FULL'
          AND os.entry_createddate BETWEEN TO_DATE('23-AUG-2011 00:00:00','DD-MON-YYYY HH24:MI:SS') AND TO_DATE('27-AUG-2011 23:59:59','DD-MON-YYYY HH24:MI:SS') )
group by LAST_DAY(TRUNC(to_timestamp(os.requestdatetime, 'yyyymmddhh24:mi:ss.ff4'))),
os.acctnum,ol.sourcecode,ol.sourcename) mrg_query
ON (ods_av_summary_bysrccd.acctnum = mrg_query.acctnum AND
ods_av_summary_bysrccd.summary_date=mrg_query.summary_date AND
ods_av_summary_bysrccd.sourcecode=mrg_query.sourcecode)
WHEN NOT MATCHED THEN
INSERT (SUMMARY_date,ACCTNUM,SOURCECODE,SOURCENAME,CNT_ARTICLEVIEW,ENTRY_LASTUPDATEDDATE)
VALUES(mrg_query.summary_date,mrg_query.acctnum,mrg_query.sourcecode,mrg_query.sourcename,
mrg_query.cnt_articleview,sysdate)
WHEN MATCHED THEN
UPDATE SET ods_av_summary_bysrccd.cnt_articleview=
CASE WHEN NVL('INCR','INCR') = 'FULL' THEN mrg_query.cnt_articleview
ELSE ods_av_summary_bysrccd.cnt_articleview+mrg_query.cnt_articleview
END,
ods_av_summary_bysrccd.entry_lastupdateddate=sysdate;My Explain Plan:
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 268591246
| Id  | Operation                                 | Name                      | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     | Pstart| Pstop |
|   0 | MERGE STATEMENT                           |                           |     1 |   456 |       |     3   (0)| 00:00:01 |       |       |
|   1 |  MERGE                                    | ODS_AV_SUMMARY_BYSRCCD    |       |       |       |            |          |       |       |
|   2 |   VIEW                                    |                           |       |       |       |            |          |       |       |
|   3 |    NESTED LOOPS OUTER                     |                           |     1 |   417 |       |     3   (0)| 00:00:01 |       |       |
|   4 |     VIEW                                  |                           |     1 |   360 |       |     5 (100)| 00:00:01 |       |       |
|   5 |      SORT GROUP BY                        |                           |     1 |    73 |   595M|            |          |       |       |
PLAN_TABLE_OUTPUT
|*  6 |       FILTER                              |                           |       |       |       |            |          |       |       |
|*  7 |        HASH JOIN                          |                           |  6975K|   485M|  3944K| 17594   (1)| 00:03:32 |       |       |
|   8 |         TABLE ACCESS FULL                 | ODS_MASTER_SOURCECODE     | 84021 |  2953K|       |   273   (1)| 00:00:04 |       |       |
|*  9 |         TABLE ACCESS BY GLOBAL INDEX ROWID| ODS_ARTICLE_VIEWS         |  7007K|   247M|       |   826   (0)| 00:00:10 |    33 |    33 |
|* 10 |          INDEX FULL SCAN                  | IDX_AV_ACCTNUM            |    25M|       |       |    26   (0)| 00:00:01 |       |       |
|  11 |     TABLE ACCESS BY GLOBAL INDEX ROWID    | ODS_AV_SUMMARY_BYSRCCD    |     1 |    57 |       |     3   (0)| 00:00:01 | ROWID | ROWID |
|* 12 |      INDEX UNIQUE SCAN                    | ODS_AV_SUMMARY_BYSRCCD_PK |     1 |       |       |     2   (0)| 00:00:01 |       |       |
Predicate Information (identified by operation id):
PLAN_TABLE_OUTPUT
   6 - filter(NULL IS NOT NULL)
   7 - access("OS"."SOURCECODE"="OL"."SOURCECODE")
   9 - filter("OS"."REQUESTDATETIME" IS NOT NULL AND "OS"."ENTRY_CREATEDDATE">=TO_DATE(' 2011-08-23 00:00:00', 'syyyy-mm-dd
              hh24:mi:ss') AND "OS"."ENTRY_CREATEDDATE"<=TO_DATE(' 2011-08-27 23:59:59', 'syyyy-mm-dd hh24:mi:ss') AND UPPER("OS"."SUCCESS_IND")='S')
  10 - filter("OS"."ACCTNUM" IS NOT NULL)
  12 - access("ODS_AV_SUMMARY_BYSRCCD"."SUMMARY_DATE"(+)=INTERNAL_FUNCTION("MRG_QUERY"."SUMMARY_DATE") AND
              "ODS_AV_SUMMARY_BYSRCCD"."ACCTNUM"(+)="MRG_QUERY"."ACCTNUM" AND "ODS_AV_SUMMARY_BYSRCCD"."SOURCECODE"(+)="MRG_QUERY"."SOURCECODE")
Note
PLAN_TABLE_OUTPUT
   - dynamic sampling used for this statement

Answer 1

Hi Toon,
Thanks for the quick resolution. I went back and verified the table's colunm details and it has a NOT NULL constraint.
Regards,
Chaitanya
P.S: Is it ok if I ask you for some help regarding a production issue I have been encountering since 15 days but haev no clear resolution yet about what/why is the reason (the said issue is neither uniform nor regular - its affecting some modules and happening on some days - i shall give the full details if you are willing to have a look) - i shall start a new post or email you directly - yur convenience.