Index Usage Depends On Columns Selected
Mar 6, 2013
somehow cannot understand why index is not used
in Oracle Database 11g Release 11.2.0.3.0 - 64bit Production
1. Included only indexed column and got a perfect plan
explain plan for2 select s.x_cnt
3 from reported_summary s
4 where s.x_cnt>0;
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2674489506
-------------------------------------------------------
| Id | Operation | Name | Cost (%CPU)|
-------------------------------------------------------
| 0 | SELECT STATEMENT | | 306 (8)|
|* 1 | INDEX FAST FULL SCAN| S_NUI01 | 306 (8)|
-------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("s"."x_CNT">0)
2. Included some other column and got TABLE ACCESS FULL
explain plan for2 select s.x_cnt,s.ru_id
3 from reported_summary s
4 where s.x_cnt>0;
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2142873335
---------------------------------------------------------------
| Id | Operation | Name | Cost (%CPU)|
---------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2421 (3)|
|* 1 | TABLE ACCESS FULL| REPORTED_SUMMARY | 2421 (3)|
---------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("s"."x_CNT">0)
3. Included all other columns and got TABLE ACCESS FULL as well explain plan for2 select s.x_cnt,s.* 3 from reported_summary s 4 where s.x_cnt>0;
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2142873335
---------------------------------------------------------------
| Id | Operation | Name | Cost (%CPU)|
---------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2421 (3)|
|* 1 | TABLE ACCESS FULL| REPORTED_SUMMARY | 2421 (3)|
---------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("s"."x_CNT">0)
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Jul 14, 2012
In my page, I have two items(type Popup LOV): P2_APP and P2_MOD and I've created two LOVs for each item. What I want is that when I select one value in first LOV in second LOV I'll get data that is related with select value in first LOV.
My table logic in database is ok, and select statements are alright.
I think that select statement in second LOV is not fetching data from first LOV item:
select MOD_NAME as display_value, MOD_CODE as return_value
from MODS
where APPLICATION= *:P2_APP* <-------- this is first LOV item with data previously selected
order by 1
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Apr 14, 2012
I have a requirement where the user input values will be passed as comma separated string to backend, which is queried against the table using instr. But the index present on the table is not using the index , due to the instr function.How can I create a index in such a way that The instr function uses it.
CREATE TABLE TEST_IDX
(
CCN VARCHAR2(10 CHAR),
SKU_NUM VARCHAR2(10 CHAR),
MOD VARCHAR2(10 CHAR),
SKU_STATUS VARCHAR2(2 CHAR),
RPT_FLAG VARCHAR2(2 CHAR),
CYCLE_AS_OF_DATE DATE,
SMP_IDENTIFIER NUMBER,
MEASURE_NAME VARCHAR2(100 CHAR)
);
CREATE INDEX TEST_IDX1 ON TEST_IDX
(CCN, SMP_IDENTIFIER, MOD, CYCLE_AS_OF_DATE, RPT_FLAG,
MEASURE_NAME);
The below query is going for full table scan due to this.
select * from test_idx where (INSTR (','||'E10000'||',', ',' || ccn || ',') <> 0 OR 'E10000' = 'DEFAULT')
and mod='90396' and rpt_flag='O' and smp_identifier=2
how to recreate the above index so that these queries uses this index.
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Feb 1, 2012
I have index on column column1 and because of the nvl, the optimizer is not picking up the index
How can I restructure the query to avoid nvl giving same result using index on column1?
now column1 and column2 are varchar2 fields here
where nvl(column1,'*')=(nvl(:param1,nvl(column2,'*'))
can I use case statement like
case when column>'' then .. stuckup here
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Dec 16, 2011
I am having a requirement like below,
Scene 1:
If duplicate records found for SSN,BWE with SAME DATE_CREATED than take the record with HIGHEST DATE_MODIFIED.
Table Structure:
SSN BWE DATE_CREATE DATE_MODIFIED
123 01-JAN-2008 02-JAN-2009 03-JAN-2014
123 01-JAN-2008 02-JAN-2009 03-JAN-2013
Output needed:
SSN BWE DATE_CREATE DATE_MODIFIED
123 01-JAN-2008 02-JAN-2009 03-JAN-2014
Scene 2:
If duplicate records found for SSN,BWE with different DATE_CREATED than take the record with HIGHEST DATE_CREATED.
Table Structure:
SSN BWE DATE_CREATE DATE_MODIFIED
123 01-JAN-2008 02-JAN-2009 03-JAN-2014
123 01-JAN-2008 04-JAN-2009 03-JAN-2013
Output needed:
SSN BWE DATE_CREATE DATE_MODIFIED
123 01-JAN-2008 04-JAN-2009 03-JAN-2013
How to achieve this requirement. My source data has 25 million of records like this.
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Jan 28, 2011
I came across situation where a Nullable column is not using index for 'order by' clause. I added Not Null condition in the 'where' condition but it wasn't useful. I don't wanted to make composite index with not nullable column or with constant or modify column to 'Not Null'
So I carried out test cases and during which I found that in one case the sql statement does 'fast full scan' for data access but does not use index for 'order by' sorting
here are the steps
Initially I kept the column Nullable
SQL> create sequence s5;
Sequence created.
SQL> create table t5 as select s5.nextval id,a.* from dba_objects a where rownum<1001;
Table created.
SQL> set pages 100
SQL> select column_name,nullable from user_tab_columns where table_name='T5';
SQL> create index i5 on t5(id);
Index created.
SQL> exec dbms_stats.gather_table_stats(user,'T5',cascade=>true);
PL/SQL procedure successfully completed.
exit
SQL> alter session set events '10046 trace name context forever, level 12';
select *
from
t5 where id is not null order by id
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 68 0.00 0.00 0 16 0 1000
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 70 0.01 0.00 0 16 0 1000
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 5
Rows Row Source Operation
------- ---------------------------------------------------
1000 SORT ORDER BY (cr=16 pr=0 pw=0 time=4771 us)
1000 TABLE ACCESS FULL T5 (cr=16 pr=0 pw=0 time=1157 us)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 68 0.00 0.00
SQL*Net message from client 68 49.49 49.72
********************************************************************************
select /*+ index(t i5) */ *
from
t5 t where id is not null order by id
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 68 0.00 0.00 0 150 0 1000
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 70 0.00 0.00 0 150 0 1000
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 5
Rows Row Source Operation
------- ---------------------------------------------------
1000 TABLE ACCESS BY INDEX ROWID T5 (cr=150 pr=0 pw=0 time=5167 us)
1000 INDEX FULL SCAN I5 (cr=71 pr=0 pw=0 time=3141 us)(object id 4673065)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 69 0.00 0.00
SQL*Net message from client 69 22.89 28.04
Now I modified the 'id' column to Not Null
SQL> alter table t5 modify id not null;
SQL> set pages 100
SQL> select column_name,nullable from user_tab_columns where table_name='T5';
COLUMN_NAME N
------------------------------ -
ID N
OWNER Y
OBJECT_NAME Y
SUBOBJECT_NAME Y
OBJECT_ID Y
DATA_OBJECT_ID Y
OBJECT_TYPE Y
CREATED Y
LAST_DDL_TIME Y
TIMESTAMP Y
STATUS Y
TEMPORARY Y
GENERATED Y
SECONDARY Y
14 rows selected.
select *
from
t5 order by id
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.01 0 29 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 68 0.00 0.00 0 16 0 1000
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 70 0.01 0.01 0 45 0 1000
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 5
Rows Row Source Operation
------- ---------------------------------------------------
1000 SORT ORDER BY (cr=16 pr=0 pw=0 time=2398 us)
1000 TABLE ACCESS FULL T5 (cr=16 pr=0 pw=0 time=1152 us)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 68 0.00 0.00
SQL*Net message from client 68 37.74 37.91
********************************************************************************
select /*+ index(t i5) */ *
from
t5 t order by id
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 68 0.00 0.00 0 150 0 1000
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 70 0.00 0.00 0 150 0 1000
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 5
Rows Row Source Operation
------- ---------------------------------------------------
1000 TABLE ACCESS BY INDEX ROWID T5 (cr=150 pr=0 pw=0 time=4166 us)
1000 INDEX FULL SCAN I5 (cr=71 pr=0 pw=0 time=3142 us)(object id 4673065)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 68 0.00 0.00
SQL*Net message from client 68 8.28 8.45
select id
from
t5 order by id
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 68 0.00 0.00 0 6 0 1000
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 70 0.00 0.00 0 6 0 1000
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 5
Rows Row Source Operation
------- ---------------------------------------------------
1000 SORT ORDER BY (cr=6 pr=0 pw=0 time=1342 us)
1000 INDEX FAST FULL SCAN I5 (cr=6 pr=0 pw=0 time=1093 us)(object id 4673065)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 68 0.00 0.00
SQL*Net message from client 68 1.88 1.89
Questions are
1) Why adding 'where id is not null wasn't enough for the index to get used in 'order by'?
2) While we got 'fast full scan' why index wasn't used for 'order by' clause?
3) Do we need the indexed column in where clause for being used in 'order by clause' too?
4) Do we need 'order by' clause if we are selecting only the indexed column with sequence generated values?
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Apr 4, 2011
I am running a fairly busy Oracle 10gR2 DB, one of the tables has about 120 columns and this table receives on average 1500 insertions per second. The table is partitioned and the partitioning is based on the most important of the two timestamp columns. There are two timestamps, they hold different times.
Out of these 120 columns, about 15 need to be indexed. Out of the 15 two of them are timestamp, at least one of these two timestamp columns is always in the where clause the queries.
Now the challenge is, the queries we run can have any combination of the 13 other columns + one timestamp. In reality the queries never have more than 7 or 8 columns in the where clause but even if we had only 4 columns in the where clause we would still have the same problem.
So if I create one concatenated index for all these columns it will not be very efficient because after the 4th or 5th column the sorting would no longer be very useful and I believe the optimiser would simply not use the rest of the index. So queries that use the leading columns of the index in sequence work well, but if I need to query the 10th column the I have performance issues.
Now, if I create multiple single column indexes oracle will have to work a lot harder to maintain all these indexes and it will create performance issues (I have tried that). Besides, if I have multiple single column indexes the optimiser will do nested loops twice or three times and will hit only the first few columns of the where clause so I think it will kind of be the same as the long concatenated index.
What I am trying to do is exactly what the Bitmap index would do, it would be very good if I could use the AND condition that a Bitmap index uses. This way I could have N number of single column indexes which the optimiser could pick from and serve the query with exactly the ones it needs. But unfortunately using the Bitmap index here is not an option given the large amount of inserts that I get on this table.
I have been looking for alternatives, I have considered creating multiple shorter concatenated indexes but this still would not address the issue since many queries would still not be served properly and therefore would take a very long time to complete.
What I had in mind would be some sort of multidimensional index, I am not even sure if such thing exists. But essentially it would be some sort of index that could serve a query efficiently regardless of the fact that the where clause has the 1st, 3rd and last columns of the index.
So considering how widely used Oracle is and how many super large databases there are out there, this problem must be common.
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Nov 23, 2012
From the previous forums i came to know about the "FILLER" option to skip any columns from loading into table.
In my case,i have columns say: col1,col2,col3,col4.....coln
Here i want to load only col3 and col4 and skip rest of the columns.I don't want to use FILLER option for each "n" number of columns to be skipped.Instead is there any options to load only the required 2 columns.
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Aug 1, 2012
Env: RHEL 5.8 RAC 11.2.0.2
I'm currently moving an IOT from one database to another using expdp/imdp. The IOT is non-partitioned and about 100GB in size containing ~1,1 billion rows.
The dumpfile contains nothing else but the IOT. I'm importing with no special parameters, no pre-created IOT, just ordinary dumpfile import. (impdp username/password dumpfile=impdp:iot.dmp nologfile=y )
During import I got unable to extend TEMP errors from impdp.
ORA-39171: Job is experiencing a resumable wait.
ORA-01652: unable to extend temp segment by 128 in tablespace TEMP
ORA-39171: Job is experiencing a resumable wait.
ORA-01652: unable to extend temp segment by 128 in tablespace TEMP
I had to add 2 additional files to my Temp tablespace (total 96GB of temp) before the import could finish off.
Is this temp usage to be expected when importing IOT's ?
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Dec 19, 2012
We have built an interactive report based on dynamic query. Normally, all the selected columns are shown in "Display" Section of the interactive report. We have a requirement to move some of the columns to the "Do not Display" when the search is done. Is it possible to do it programmatically ?
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Jun 28, 2013
Is their any query to find cpu usage & memory usage of all the queries currently running on DB?
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Dec 17, 2012
Suppose i have two columns ID and Status (or any number of columns ) belongs to table customer. Now I want to create below index
Ex. create index test1 on customer (ID , Status )
But before creating this index i want to check that whether there is already index on these 2 columns ? May be by other name ?
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Sep 13, 2013
I have a table with a non-unique index consisting of three columns. The first column is not null while the remaining two are nullable. Queries using this index will chiefly be made in two ways.
1. Column one and two having values. Column three is null.
2. Column one and thre having values. Column two is null.
In both cases I expect range scan will be used since it's non-unique. In the first case the scan will be on values in column one and two. But what happens in case two. Will the range be on colum one, column two(being null) and cxolumn three? Or will it be on just column one since the second column is null? I have done some testing. I can see , using EXPLAN PLAN, that range scan is used in both cases. how the index is used?
Is there any other drawbacks with an index like this?
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Mar 5, 2012
I have two tables like below-
CREATE TABLE prod_vendor_record (
vendor_record_seq_no NUMBER NOT NULL,
study_seq_no NUMBER NOT NULL,
vendor_subject_seq_no NUMBER NULL,
control_dataset_seq_no NUMBER NOT NULL,
checksum NUMBER NOT NULL,
processing_flag VARCHAR2(1) NULL,
[code]....
and executing below query on those tables-
insert into prod_temp_vendor(vendor_record_seq_no,checksum,rownumber,transaction_type,iu_flag)
select vr.vendor_record_seq_no, tvr.checksum, tvr.rownumber, tvr.transaction_type, 'U' from
prod_vendor_record vr, prod_temp_vendor_record_20000 tvr
where vr.study_seq_no=25707
and vr.control_dataset_seq_no=3910
and vr.key_hash=tvr.key_hash
and dbms_lob.compare(vr.key_col_val, tvr.key_col_val) = 0
and tvr.error_flag is null;
let me know on which columns of PROD_VENDOR_RECORD table to apply index to make processing faster. As I tried to build index like below-
CREATE INDEX idx_prod_vendor_record
ON prod_vendor_record (
study_seq_no,
control_dataset_seq_no,
key_hash
)
/
But it is not being used by above query (see execution plan)
--------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------------------------------------------------------------------
| 0 | INSERT STATEMENT | | | | 5168 (100)| | | | |
| 1 | PX COORDINATOR | | | | | | | | |
| 2 | PX SEND QC (RANDOM) | :TQ10002 | 212 | 445K| 5168 (1)| 00:01:03 | Q1,02 | P->S | QC (RAND) |
[code]....
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Dec 14, 2010
I have been reading Oracle documentaion about access paths, got strucked at the concept 'Leading columns in index'. what is meant by 'Leading columns of an index', how to find/judge them that they are leading columns.
The url where I am reading is[URL]...
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Feb 24, 2012
I have a table TP having following data (Dashes used for space as i am unable to have proper alignment)
ID1-----TOT
1 ------- 5
2 ------- 7
I need a query that repeat the records depending on the field TP.TOT
e.g.
ID1 -----TOT
1 ------- 5
1 ------- 5
1 ------- 5
1 ------- 5
1 ------- 5
2 ------- 7
2 ------- 7
2 ------- 7
2 ------- 7
2 ------- 7
2 ------- 7
2 ------- 7
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Jul 19, 2012
What should be the order of columns while creating b-tree non-unique index.
Low cardinality first
or
Hight cardinality first
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Mar 30, 2006
we have oracle 8i/win nt. (Prod Server running 24 X7)
On doing a explain plan on long running queries. i realized a couple of columns (that were used in the WHERE condition, were not having any indexes.)
More importantly, here we do not have a Test environment.
I would like to know if i can go ahead and create indexes for those 2 columns by issuing
CREATE INDEX index_name on table_name(Column_name);
on our PDB.
Would this be of any impact on our PDB? Do i check anything more prior to building these indexes. or Do have i create them at a down time of PDB.
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Jun 21, 2012
We have a big problem in the underlying devices that ASM disk groups depends on. We have SAN disks (EMC DMX) presented to us as /dev/sda, /dev/sdb, etc.These disks have actually multipath setup. For example, - /dev/emcpowera has two different paths as:
1./dev/sda
2./dev/sdp
We were using the direct path /dev/sda to format the disk (as fdisk /dev/sda), and then used oracleasm to create disks (oracleasm createdisk ASMDISKDATA0 /dev/sda1). Then, ASM disk groups were created with those lables (volumes), and then database was created using the ASM disk groups.
Now our platform folks are telling us that we should use the multipath /dev/emcpowera instead of direct path /dev/sda as the direct path is not guaranteed across reboot.
So the questions are:
1.Is there a way to re-link the disk group to asm disk to the multipath devices (/dev/emcpowera1 instead of /dev/sda1)?
2.Is this even an issue for ASM? If the /dev/sda fails after reboot, can Oracle ASM automatically discover the other path /dev/sdp to the physical EMC disk?
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Jan 15, 2013
I have been using With for many queries for readability. This most recent query seemed to be taking a bit longer to run and I didn't think much of it until a colleague showed me their version (totally different sql statement) which ran faster, but seemed more complicated and had more lines of code. I noticed that the other version did not use with. I moved the sql of the with into the join and the query ran faster dropping from 30 seconds to 798 msecs. The question is am I sacrificing speed for readability by using With, or it really depends on the overall sql statement.
Here is the query using WITH:
with prev as
(
select person_uid, id, name, academic_period,
case when enrolled_ind = 'Y' and registered_ind = 'N' and student_status = 'AS' then 0 else 1 end as enreg_stat,
[Code]....
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Jun 15, 2012
Is anyway to create function based index for group function columns.
For example
select max(timestamp),min(age),averge(sal).... ... .. from tab;
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Jun 27, 2012
I am on 11.2.0.3 Enterprise Edition. We are using the new feature "Composite Domain Index" for a Domain index on a very large table (>250.000.000 rows). It really works with mixed queries. We added two number columns using FILTER BY.We have lots of DML on this table. Therefore, we are executing synchronize and optimize once the week. The synch behaves pretty normal. But "optimize_index" takes a very very long time to complete. I have switsched on 'logging' for the optimize process. The $I table takes some time but is finished normally. But the optimization of the $S table (that is the table created for the CDI feature) is running over 12 hours now - and far from being finished. From the logfile, I can see that it optimizes 1000 rows every 20 minutes. Here is the output of the logfile:
Oracle Text, 11.2.0.3.0
14:33:05 06/26/12 begin logging
14:33:05 06/26/12 event
14:33:05 06/26/12 process $N for optimize: SEQDEV.GEN_GES_DESCRIPTION_CTX_I
14:33:16 06/26/12
14:33:16 06/26/12
[code]....
I haven't found a recommendation from Oracle not to use "optimize_index" for Domain Indexes with CDI. But in my case, it would be much faster just to drop and recreate the Domain Index in question.
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Jun 28, 2011
I have a huge table (about 60 gb) partition over range. The index on this table is global index created on 4 columns together. I have a query which is running very slowly. The explain plan is showing the use of this global index.Explain plan is not showing pstart and pend because the index is global.
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Jun 23, 2011
I have a global index and I want to convert it to local index.Is there a way to recreate local index with out dropping the global index.
I can create a local index first and then drop the global index. But is there a way to create it with out dropping the global index, just convert it.
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Nov 29, 2010
I am facing the error "ORA-01502: index or partition of such index is in unusable state " while loading the text data using
sql loader with direct path (direct = Y ,rows = 10000) option. Table consists an composite non unique index. If I query the dba indexes for the effected index it shows the index status as VALID. There was no maintaince done on the effected table or index. I have tried loading the same data using conventional path but didn't found any issues for the same.
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Nov 19, 2010
I have a query which had a join:
a.c1=b.c1 and a.c2=@var
where @var is user supplied input at runtime...We had a index on a.c2 . The CBO would use this index to generate an opitimised query plan.We found some records from table "b" were dropping due to inner join. So we made a change in join. It'd be like
a.c1(+)=b.c1 and nvl(a.c2,@var)=@var
This query is no longer using the index, instead its doing a full table scan causing the query to slowdown.I have tried creating index on nvl(a.c2,'31-dec-9999')
But the CBO won't use it.Anyway to create index on this col so that full table scan can be avoided?
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Aug 9, 2013
How to force an index if the table not using the index?
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Aug 27, 2012
We have occurrences of enq : TX - index contentions in the database. Using the SQL ID, we have identified the INSERT statement and the table which they are trying to insert.
This table has almost 25 different indexes, some of which are unique as well.I am wondering how to identify the actual index causing issue, out of these 25 indexes.
Is there any way to pin point to the name of index which is causing the lock?My plan is, once the index is identified, I would like to check the extents and inittrans and other attributes of this index to fix.
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Apr 21, 2013
There is a simple table prod having a column crlf.i did the following
Quote:
SQL> update prod set crlf=null;
716 rows updated.
SQL> commit;
Commit complete.
SQL> select * from prod where crlf=null;
no rows selected
why NO row selected against last query?
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Oct 20, 2011
There is an 'emp' table with a column name as 'mgr' with datatype 'number'. following is the detailed description of the table:
SQL> desc emp;
Name Null? Type
----------------------------------------- -------- ---------------------------
EMPNO NOT NULL NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)
Now when I run the 'select mgr from emp e;' query the output which I get is:
7902
7698
7698
7839
7698
7839
7839
7566
7698
7788
7698
7566
7782
Note: One value in between here is null, the required to me is that I want to print a character value 'President' in place of null .
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