Query not using index when using 'or' clause

I have a problem with something I can't understand about indexes in Oracle 11g.
We can create test data with:
create table test2(field1 varchar2(100),field2 varchar2(100),field3 number,field4 varchar2(100));
create index test2_idx1 on test2(upper(field1));
create index test2_idx1b on test2(field1);
create index test2_idx2 on test2(field3);
DECLARE
j NUMBER :=1;
BEGIN
FOR i IN 1..500000
LOOP
INSERT
INTO test2
(field1,field2, field3, field4)
VALUES
('field1='||i,'a', j, 'i' );
IF (i mod 1000)=0 THEN
j := j+1;
END IF;
END LOOP;
COMMIT;
END;
EXEC DBMS_STATS.GATHER_TABLE_STATS ('system', 'test2');
Then I make some explain plans which result I can't understand
Query 1:
SELECT * FROM test2 WHERE field3=1;
Explain plan:
Explain plan for query 01
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1003 | 28084 | 10 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TEST2 | 1003 | 28084 | 10 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | TEST2_IDX2 | 1003 | | 5 (0)| 00:00:01 |
Everything OK here. Index is used.
Query 2:
SELECT * FROM test2 WHERE upper(field1)='FIELD1=1';
Explain plan
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 28 | 4 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TEST2 | 1 | 28 | 4 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | TEST2_IDX1 | 1 | | 3 (0)| 00:00:01 |
Everything OK again. Index is used.
Query 3:
SELECT /*+ USE_CONCAT */ * FROM test2 WHERE field1='FIELD1=1' OR field3=1;
Explain plan
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1004 | 28112 | 14 (0)| 00:00:01 |
| 1 | CONCATENATION | | | | | |
| 2 | TABLE ACCESS BY INDEX ROWID| TEST2 | 1 | 28 | 4 (0)| 00:00:01 |
|* 3 | INDEX RANGE SCAN | TEST2_IDX1B | 1 | | 3 (0)| 00:00:01 |
|* 4 | TABLE ACCESS BY INDEX ROWID| TEST2 | 1003 | 28084 | 10 (0)| 00:00:01 |
|* 5 | INDEX RANGE SCAN | TEST2_IDX2 | 1003 | | 5 (0)| 00:00:01 |
Indenxes are used in concatenation. No problem again.
Query 4:
SELECT /*+ USE_CONCAT */ * FROM test2 WHERE upper(field1)='FIELD1=1' OR field3=1;
Explain plan
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1004 | 28112 | 641 (4)| 00:00:08 |
| 1 | CONCATENATION | | | | | |
|* 2 | TABLE ACCESS FULL | TEST2 | 1 | 28 | 631 (4)| 00:00:08 |
|* 3 | TABLE ACCESS BY INDEX ROWID| TEST2 | 1003 | 28084 | 10 (0)| 00:00:01 |
|* 4 | INDEX RANGE SCAN | TEST2_IDX2 | 1003 | | 5 (0)| 00:00:01 |
Here my problem arises. Why is test2_idx1 not being used? Is it because it is a function index? Is there any workaround in this cases?
Thanks a lot in advance.

Interesting. A "workaround" which I thought first was:
SELECT /*+ USE_CONCAT */ * FROM test2 WHERE upper(field1)='FIELD1=1'
UNION ALL
SELECT /*+ USE_CONCAT */ * FROM test2 WHERE field3=1;
| Id | Operation                    | Name       | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT             |            | 1001 | 28042 |    15 (74)| 00:00:01 |
|   1 | UNION-ALL                   |            |       |       |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| TEST2      |     1 |    42 |     4   (0)| 00:00:01 |
|* 3 |    INDEX RANGE SCAN          | TEST2_IDX1 |     1 |       |     3   (0)| 00:00:01 |
|   4 |   TABLE ACCESS BY INDEX ROWID| TEST2      | 1000 | 28000 |    11   (0)| 00:00:01 |
|* 5 |    INDEX RANGE SCAN          | TEST2_IDX2 | 1000 |       |     5   (0)| 00:00:01 |
-------------------------------------------------------------------------------------------   But I do not like using UNION for such tricks. So I thought, what would ORACLE do without hint?
SELECT * FROM test2 WHERE upper(field1)='FIELD1=1' or field3=1;
| Id | Operation                        | Name       | Rows | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT                 |            | 1001 | 42042 |   176   (0)| 00:00:03 |
|   1 | TABLE ACCESS BY INDEX ROWID     | TEST2      | 1001 | 42042 |   176   (0)| 00:00:03 |
|   2 |   BITMAP CONVERSION TO ROWIDS    |            |       |       |            |          |
|   3 |    BITMAP OR                     |            |       |       |            |          |
|   4 |     BITMAP CONVERSION FROM ROWIDS|            |       |       |            |          |
|* 5 |      INDEX RANGE SCAN            | TEST2_IDX2 |       |       |     5   (0)| 00:00:01 |
|   6 |     BITMAP CONVERSION FROM ROWIDS|            |       |       |            |          |
|* 7 |      INDEX RANGE SCAN            | TEST2_IDX1 |       |       |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------------------------- Thist looks perfect to me. (Please ignore the "higher" cost on the second plan. On your real data, it should be faster. Is it?)

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Edited by: remaï on Apr 1, 2009 4:08 PM

What version of oracle you have? CBO work is different in 9i and 10g.
Usually cost based optimizer do not want to use index for >< condition with binding variables because optimizer can not use statistic to determine selectivity, and by default selectivity of <> operators is low.
(As I remember '>' selectivity by default is 5%, you have two conditions > and <, therefore resulting selectivity will be 0.05*0.05=0.0025 as two independent events, but selectivity of other conditions
ORDER_MVTS.MVT_TYPE = 'DELIVERY' or ORDER.CUSTOMER_CODE = 'ADIDAS' looks much better for CBO)
The best solution I see is do not use binding variables. Actually your query looks as searching query, which executes not so often, therefore you will not have perfomance win along of skipping execution plan creation.
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9 This plan step accepts a row set (its only child) and sorts it in preparation for a merge-join operation.
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1 ERMS.COURSE TABLE ACCESS [FULL]
3 ERMS.STUDENTS TABLE ACCESS [BY INDEX ROWID]
2 ERMS.INDEX_STUDENTS_CAMPUS_CODE INDEX [RANGE SCAN]
5 ERMS.SYS_C007065 INDEX [RANGE SCAN]
9 SORT [JOIN]
8 ERMS.STUDENT_DEGREE TABLE ACCESS [FULL]
Step # Description
1 This plan step retrieves all rows from table COURSE.
2 This plan step retrieves one or more ROWIDs in ascending order by scanning the B*-tree index INDEX_STUDENTS_CAMPUS_CODE.
3 This plan step retrieves rows from table STUDENTS through ROWID(s) returned by an index.
4 This plan step joins two sets of rows by iterating over the driving, or outer, row set (the first child of the join) and, for each row, carrying out the steps of the inner row set (the second child). Corresponding pairs of rows are tested against the join condition specified in the query's WHERE clause.
5 This plan step retrieves one or more ROWIDs in ascending order by scanning the B*-tree index SYS_C007065.
6 This plan step joins two sets of rows by iterating over the driving, or outer, row set (the first child of the join) and, for each row, carrying out the steps of the inner row set (the second child). Corresponding pairs of rows are tested against the join condition specified in the query's WHERE clause.
7 This plan step accepts a row set (its only child) and sorts it in preparation for a merge-join operation.
8 This plan step retrieves all rows from table STUDENT_DEGREE.
9 This plan step accepts a row set (its only child) and sorts it in preparation for a merge-join operation.
10 This plan step accepts two sets of rows sorted on the join key. By walking both sets of rows in the order of the join key, every distinct pair of rows satisfying the join condition in the WHERE clause is found through a single pass of the row sets.
11 This plan step designates this statement as a SELECT statement.

How to use index, when query has decode/case

Hi,
I have the following query
i have a index on party_id,party_type_Code in the zx_party_tax_profile table But this index is not used as Iam using a decode on the columns of the zx_party_tax_profile table,
Is there any way i can rewrite the query so that it uses index
sELECT /*+ INDEX(ZX_PARTY_TAX_PROFILE_U2) */ party_tax_profile_id FROM (SELECT
ThirdPartyTaxProfileEO.SUPPLIER_FLAG,
ThirdPartyTaxProfileEO.CUSTOMER_FLAG,
ThirdPartyTaxProfileEO.SITE_FLAG,
ThirdPartyTaxProfileEO.PARTY_TAX_PROFILE_ID,
ThirdPartyTaxProfileEO.PARTY_ID,
ThirdPartyTaxProfileEO.REP_REGISTRATION_NUMBER,
ThirdPartyTaxProfileEO.OBJECT_VERSION_NUMBER,
ThirdPartyTaxProfileEO.REGISTRATION_TYPE_CODE,
ThirdPartyTaxProfileEO.COUNTRY_CODE,
ThirdPartyTaxProfileEO.MERGED_TO_PTP_ID,
ThirdPartyTaxProfileEO.MERGED_STATUS_CODE,
ThirdPartyTaxProfileEO.PROGRAM_APP_NAME,
ThirdPartyTaxProfileEO.PROGRAM_NAME,
PartyPEO.PARTY_NAME,
PartyPEO.PARTY_ID AS PARTY_ID1,
PartyPEO.PARTY_NUMBER,
decode(ThirdPartyTaxProfileEO.CUSTOMER_FLAG,
'Y',decode(ThirdPartyTaxProfileEO.SUPPLIER_FLAG,
'Y', 'SC',
'C'),
decode(ThirdPartyTaxProfileEO.SUPPLIER_FLAG,
'Y', 'S',
NULL)
) AS PARTY_USAGE,
ThirdPartyTaxProfileEO.REP_REGISTRATION_NUMBER AS TAX_REG_NUMBER,
LkupPartyUsage.MEANING AS PARTY_USAGE_DESC,
PartyPEO.PARTY_NAME AS PARTY_FULL_NAME,
PartyPEO.ADDRESS1||','||
PartyPEO.ADDRESS2||','||
PartyPEO.ADDRESS3||','||
PartyPEO.CITY||','||
PartyPEO.postal_code||','||
PartyPEO.COUNTRY AS ADDRESS,
PartyPEO.COUNTRY AS COUNTRY_CODE_TCA,
TerritoryPEO.TERRITORY_SHORT_NAME AS COUNTRY_NAME,
PartyPEO.JGZZ_FISCAL_CODE AS TAX_PAYER_ID,
PartyPEO.DUNS_NUMBER_C AS DUNS_NUMBER,
PartyPEO.Party_Number as Party_Num_Calc,
null as REGISTRATION_TYPE_NAME,
null as ROUNDING_LEVEL_NAME,
null as ROUNDING_RULE_NAME,
null as COUNTRY_NAME_PTP,
'ZX_PARTY_TAX_PROFILE' as TAX_REPORTING_ENTITY_CODE
FROM ZX_PARTY_TAX_PROFILE ThirdPartyTaxProfileEO,
HZ_PARTIES PartyPEO,
FND_LOOKUP_VALUES_VL LkupPartyUsage,
FND_TERRITORIES_VL TerritoryPEO
WHERE ThirdPartyTaxProfileEO.PARTY_ID = PartyPEO.PARTY_ID AND
LkupPartyUsage.LOOKUP_CODE = decode(ThirdPartyTaxProfileEO.CUSTOMER_FLAG,
'Y',decode(ThirdPartyTaxProfileEO.SUPPLIER_FLAG,
'Y', 'SC',
'C'),
decode(ThirdPartyTaxProfileEO.SUPPLIER_FLAG,
'Y', 'S',
NULL)
) AND
PartyPEO.COUNTRY = TerritoryPEO.Territory_Code (+) AND
LkupPartyUsage.LOOKUP_TYPE = 'ZX_TP_PARTY_USAGE'
ORDER BY UPPER(PARTY_FULL_NAME)) QRSLT WHERE UPPER(PARTY_NAME) IS NOT
NULL
Any help will be appreciated

You can rewrite your where clause to not use decode or case statements e.g. this:
AND LkupPartyUsage.LOOKUP_CODE = DECODE( ThirdPartyTaxProfileEO.CUSTOMER_FLAG
                            , 'Y', DECODE( ThirdPartyTaxProfileEO.SUPPLIER_FLAG, 'Y', 'SC', 'C' )
                                 , DECODE( ThirdPartyTaxProfileEO.SUPPLIER_FLAG, 'Y', 'S', NULL ) )
                                 )can be rewritten to this:
and (
      ( ThirdPartyTaxProfileEO.CUSTOMER_FLAG = 'Y' AND
          ((ThirdPartyTaxProfileEO.SUPPLIER_FLAG = 'Y' AND LkupPartyUsage.LOOKUP_CODE = 'SC') or
            ThirdPartyTaxProfileEO.SUPPLIER_FLAG != 'Y' AND LkupPartyUsage.LOOKUP_CODE = 'C')) or
      ( ThirdPartyTaxProfileEO.CUSTOMER_FLAG != 'Y' AND
          ((ThirdPartyTaxProfileEO.SUPPLIER_FLAG = 'Y' AND LkupPartyUsage.LOOKUP_CODE = 'S') or
            ThirdPartyTaxProfileEO.SUPPLIER_FLAG != 'Y' AND LkupPartyUsage.LOOKUP_CODE is null))
    )It's not as sussinct, but it avoids the use of functions that could be preventing the optimiser from using an index.

Query not using index when using 'or' clause

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