What is happening in this plan

Question

Hi Please take a look at the below query and its plan. The Step 9 in the Plan applies the condition (ebill.is_synced_to_orig = 0 OR ebill.is_synced_to_orig IS NULL). but since it is a index scan it only applies is_synced_to_orig = 0 condition. But ideally the other selectivity should also be considered somewhere else right. but I could not see that in the plan.
Is oracle skipping that condition?? much appreciate if someone can say what is happening in this plan for is_synced_to_orig IS NULL condition. thanks...
SELECT ebill.ebill_summary_id
FROM ebill_summary ebill INNER JOIN originator orig
ON ebill.originator_id = orig.originator_id
AND (ebill.is_synced_to_orig = 0 OR ebill.is_synced_to_orig IS NULL)
INNER JOIN entity e
ON e.entity_id = orig.entity_id
AND e.entity_type_id = 1
AND e.entity_id = 1
LEFT OUTER JOIN te_pmt_task_lock tl
ON tl.payment_request_id = ebill.ebill_summary_id
AND tl.te_task_id = 1234
AND tl.is_expired = 1
WHERE tl.payment_request_id IS NULL AND ROWNUM <= 1000;
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 56 | 16 (0)| 00:00:01 |
|* 1 | COUNT STOPKEY | | | | | |
|* 2 | FILTER | | | | | |
| 3 | NESTED LOOPS OUTER | | 1 | 56 | 16 (0)| 00:00:01 |
| 4 | NESTED LOOPS | | 1 | 47 | 2 (0)| 00:00:01 |
| 5 | NESTED LOOPS | | 1 | 43 | 1 (0)| 00:00:01 |
|* 6 | TABLE ACCESS BY INDEX ROWID| ENTITY | 1 | 4 | 1 (0)| 00:00:01 |
|* 7 | INDEX UNIQUE SCAN | ENTITIES_PK | 1 | | 0 (0)| 00:00:01 |
| 8 | TABLE ACCESS BY INDEX ROWID| EBILL_SUMMARY | 1 | 39 | 0 (0)| 00:00:01 |
|* 9 | INDEX RANGE SCAN | EBILL_IS_SYNCED_TO_ORIG_IDX | 1 | | 0 (0)| 00:00:01 |
|* 10 | TABLE ACCESS BY INDEX ROWID | ORIGINATOR | 1 | 4 | 1 (0)| 00:00:01 |
|* 11 | INDEX RANGE SCAN | ORIGINATOR_ENTITY_IDX | 1 | | 0 (0)| 00:00:01 |
|* 12 | INDEX RANGE SCAN | TEPMTTSKLCK_TSKEXPRDPYNREQ_ID | 1 | 9 | 14 (0)| 00:00:01 |
Predicate Information (identified by operation id):
1 - filter(ROWNUM<=1000)
2 - filter("TL"."PAYMENT_REQUEST_ID" IS NULL)
6 - filter("E"."ENTITY_TYPE_ID"=1)
7 - access("E"."ENTITY_ID"=1)
9 - access("EBILL"."IS_SYNCED_TO_ORIG"=0)
10 - filter("EBILL"."ORIGINATOR_ID"="ORIG"."ORIGINATOR_ID")
11 - access("ORIG"."ENTITY_ID"=1)
12 - access("TL"."TE_TASK_ID"(+)=1234 AND "TL"."IS_EXPIRED"(+)=1 AND
"TL"."PAYMENT_REQUEST_ID"(+)="EBILL"."EBILL_SUMMARY_ID")

Answer 1

Well, if the column is declared as NOT NULL and you ask for all rows such that the column = 1 OR it is null then really you are asking for all data where the column = 1 since by definition, there cannot be nulls (the NOT NULL constraint on the column prohibits NULL data from occurring).
Make sense?
Now, i'm not saying that's what your issue is, but since i haven't seen what your tables look like ... it's as good a guess as i can muster.