Performance Tuning :: How To Overcome Rownum Clause From Select
Dec 27, 2010
high number of executions of specific types of queries which is using only rownum clause. For exam.
select ani, rowid from tbl_smschat_upuor where rownum<=:"SYS_B_0";
DB is having high number of executions of these type of queries and these when I m checking the execution plan for the same type of queries it is accessing the full table scan.
======================execution plan for above query
1000 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 91289622
--------------------------------------------------------------------------------
[code]....
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Oct 17, 2011
The following query gets input parameter from the Front End application, which User queries to get Reports.There are many drop down boxes like LOB, FAMILY, BRAND etc., The user may or may not select values from drop down boxes.
If the user select any one or more values ( against each drop down box) it has to fetch all matching values from DB. If the user does'nt select any values it has to fetch all the records, in this case application will send a value 'DEFAULT' (which is not a value in DB ) so that the DB will fetch all the records.
For getting this I wrote a query like below using DECODE, which colleague suggested that will hamper performance.From the below query all the variables V_ are defined in procedure which gets the values selected by user as a comma separated string here V_SELLOB and LOB_DESC is column in DB.
DECODE (V_SELLOB, 'DEFAULT', V_SELLOB, LOB_DESC) IN
OPEN v_refcursor FOR
SELECT /*+ FULL(a) PARALLEL(a, 5) */
*
FROM items a
WHERE a.sku_status = 'A'
[code]...
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Mar 31, 2012
This query is taking 7 hours to execute as I am retrieving data from history table dept_hist.
select count(distinct empid), e.group_nm, d.date,
from emp e, dept_hist d
where e.deptno = d.deptno
and e.up_ts > sysdate -30
[Code]...
Its taking 7 hours to execute.restructing this query.
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Apr 4, 2010
When i try to execute a query, which is organised as the below example, it retrieves data..
select * from (
select col1, col2, col3, col4....coln
from TABLE_ONE left outer join TABLE_TWO
-- some conditions and group by clause
order by 1 asc
)
where rownum <=1000;
Again if I use Column alias in the ORDER BY clause col1, the query won't retrieve data.
Also If I use ORDER BY 4 instead of ORDER BY 1, the query wont return data...
select * from (
select col1, col2, col3, col4....coln
from TABLE_ONE left outer join TABLE_TWO
-- some conditions and group by clause
order by 4 asc
)
where rownum <=1000;
The whole issue revolves around the inner ORDER BY Clause and external ROWNUM condition..If I eliminate any of the two, the query works fine...I am not sure if indexes have some role to play in it...
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Jun 4, 2013
avoid duplication of **where** clause in my query.
In my below query, **JOIN** condition is same for both the queries and **WHERE** condition also same except this clause "and code.code_name="transaction_1" In **IF ** condition only credit and debit is swapped on both queries, due to this **Credit and Debit** and this where clause "and code.code_name="transaction_1" I am duplicating the query. avoid this duplication. I am using oracle 11g
SELECT day AS business_date,
SUM(amount) AS AMOUNT,
type_amnt AS amount_type,
[Code]....
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Dec 8, 2010
There is a table in Database with millions of records and a query --- Select rowid, ANI, DNIS, message from tbl_sms_talkies where rownum<=:"SYS_B_0" ---- using the high CPU and also this query having high number of executions.
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Jul 11, 2013
Below query is degrading the performance of database. As we know that, without where clause, query do full table scan.Now, it is written to generate the sequence no.
SQL> explain plan for
2 SELECT NVL(MAX(P.NUM_SERIAL_NO), 0) + 1 FROM CNFGTR_IRDA_ENVELOPE_DTLS P
3 /
Explained.
SQL> select * from table(dbms_xplan.display());
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
Plan hash value: 3345343365
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------
[code].....
Index is not created on the column.
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Mar 2, 2011
In my below query example , i have to pass more than 4000-5000 paramter in "a1.num" in below query. what is the best way to handle this, also if I pass more than 2000 paramter , the query takes a long time to execute. How can we solve the performance issue as well how I can pass more parameter.
SELECT c1, c2,
TO_CHAR (c3, 'HH24:MI'),
c4,
c5,
[code]...
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May 1, 2008
How to avoid sort operation by an order by clause without changing the sort area size.what hints or changes should be done in query so that order by clause work faster.
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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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Jun 2, 2011
We have a person running a query and following is the explain plan
explain plan for
select distinct(extractvalue(xmltype(a.email_variables), '/CalliopeData/Attributes/HOTEL_BRAND')) as ThisBrand
from hh.t_ecomm_mem_relations a
where extractvalue(xmltype(a.email_variables), '/CalliopeData/Attributes/HOTEL_BRAND') not in (select b.code_brand from hh.t_pr_brand b)
and a.code_corr_ecat = 'PREA'
and a.status = 'S'
and a.audit_time > sysdate - 1
;
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1904775187
-------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
-------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 14 | 32018 | 25 (4)| 00:00:01 | | |
| 1 | HASH UNIQUE | | 14 | 32018 | 25 (4)| 00:00:01 | | |
|* 2 | FILTER | | | | | | | |
| 3 | PARTITION RANGE ITERATOR | | 14 | 32018 | 17 (0)| 00:00:01 | KEY | 13 |
|* 4 | TABLE ACCESS BY LOCAL INDEX ROWID| T_ECOMM_MEM_RELATIONS | 14 | 32018 | 17 (0)| 00:00:01 | KEY | 13 |
|* 5 | INDEX RANGE SCAN | X_ECOMM_MEM_RELATIONS3 | 15 | | 3 (0)| 00:00:01 | KEY | 13 |
|* 6 | INDEX FULL SCAN | I_PR_BRAND | 1 | 3 | 1 (0)| 00:00:01 | | |
-------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter( NOT EXISTS (SELECT /*+ */ 0 FROM "HH"."T_PR_BRAND" "B" WHERE
LNNVL("B"."CODE_BRAND"<>EXTRACTVALUE("XMLTYPE"."XMLTYPE"(:B1),'/CalliopeData/Attributes/HOTEL_BRAND'))))
4 - filter("A"."STATUS"='S')
5 - access("A"."AUDIT_TIME">SYSDATE@!-1 AND "A"."CODE_CORR_ECAT"='PREA')
filter("A"."CODE_CORR_ECAT"='PREA')
6 - filter(LNNVL("B"."CODE_BRAND"<>EXTRACTVALUE("XMLTYPE"."XMLTYPE"(:B1),'/CalliopeData/Attributes/HOTEL_BRAND')))
=========================
I tried not exists and some Antijoin hints in the subquery which is used in filter NOT IN. I tried minus too.
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Dec 23, 2010
I have a view, below, which does few left outer joins to the same V_MARKET view to get data i need. When I run SQL by itself, ut runs pretty fast, 2-5 seconds. But when I do "select * from V_DEPT_DATA where busines_date = '01-APR-10'", it takes more than 10 minutes to run. I added all needed indexes and still have problems with it .
CREATE OR REPLACE VIEW V_DEPT_DATA
AS
SELECT
v1.business_date ,
v1.division ,
v1.department ,
v1.account ,
en.trader ,
[code]........
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Apr 8, 2011
I'm working on a query that will show how many differents SKUs we have on-hand, how many of those SKUs have been cycle-counted, and how many we have yet to cycle-count.I've prepared a sample table and data:
CREATE TABLE SKU
(
ABC VARCHAR2(1 CHAR),
SKU VARCHAR2(32 CHAR) NOT NULL,
Lastcyclecount DATE,
[code]....
What I also want to do is select another column that will group by sku.abc and count the total number of A, B, and C SKUs where the lot.qty is > 0:
SELECT sk.abc AS "STRATA",
COUNT (DISTINCT sk.sku) AS "Total"
FROM sku sk,
(SELECT sku
FROM lot
WHERE qty > 0) item
WHERE item.sku = sk.sku(+)
GROUP BY sk.abc
Finally, I need the last column to display the DIFFERENCE between the two totals from the queries above (the difference between the "counted" and the "total"):
COUNT (DISTINCT sk.sku) - COUNT (DISTINCT s.sku)
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Jul 21, 2010
I've been examining som old queries in an existing db due to more and more problems regarding performance. The sql is used as backend for a java/jboss web application with the possibility for users to enter data. With more and more data, there starting to come complaints about the performance.
I stumbled upon a select query with an embedded cursor similar to this :
select id, name ...,
cursor(select id, sequence.... from table2),
cursor(select id, name.... from table3)
from table1
join table4 on (table1.id = table4.id)
where .....
The javacode is a prepared statement with the actual sql as a string and the content of the cursors saved in conjunction with each row.
when i use sqldeveloper to show the explain plan without the cursors, the cost is 2428
when i use sqldeveloper to show the explain plan with just 1 of the cursors, the cost is ~165000
Is there a better way to do this instead of cursors ?
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Nov 27, 2012
I am using this as a subquery within a large select statement.
(select NAME_LAST from person_name where person_id=enc.person_id and ROWNUM = 1 order by person_name_id desc) as PatFirstName
I am getting issues when i am doing rownum=1 with order by clause, what is teh right way.
when i use rownum < 2 without order y clause it is workign fine.
I would like to use order by clause.
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Sep 12, 2011
Having production system: 11.2.0.1 on Windows Server x64
Test system: 9.2.0.1 on Windows XP
Problem preface: to get all unique CASEID which should be checked up by biometric system.What i should check - all CASEs for different PERSONs having same PHONEs at least among one phone type (1..4).Real table contains little bit more than 10 million records.I made test scripts.
Below the DDL for test table creation:
------------------------------------------
-- Create CASEINFO test table
------------------------------------------
DROP TABLE CASEINFO;
CREATE TABLE CASEINFO
[code]...
Below i've put SQL/DLL to make test data.number of records inserted 2 millions.
PERSON_COUNT := #/8;
------------------------------------------
-- fill CASEINFO with sample data
------------------------------------------
DECLARE
I INTEGER;
[code]...
Below SQL select to check the data in created table.
------------------------------------------
-- Check test data counters
------------------------------------------
SELECT 'TOTAL',count(*) from CASEINFO
UNION ALL
SELECT 'LEGAL',count(*) from CASEINFO where
[code]...
The PROBLEM is that i am experiencing HUGE perfomance problems on both test and production systems with that query:
select distinct b.caseid
from CASEINFO a, CASEINFO b
where (a.person<>b.person) and (a.sex=b.sex) and
(
(a.phone1=b.phone1) or
(a.phone1=b.phone2) or
(a.phone1=b.phone3) or
[code]...
This query takes almost 90 minutes to execute.And i do not know how to avoid this.Full SQL file to make test attached.
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Sep 15, 2011
I was confused by partitioed table, when i select a partition of table, how does oracle to scan blocks? it scan all blocks of table or scan a single partition blocks only?
SQL> Explain Plan For
2 Select Count(1) From Tb_Hxl_List Partition(p_L3);
Explained.
SQL> Select * From Table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 18 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | PARTITION LIST SINGLE| | 33115 | 18 (0)| 00:00:01 |
| 3 | TABLE ACCESS FULL | TB_HXL_LIST | 33115 | 18 (0)| 00:00:01 |
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Sep 8, 2009
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Solaris: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
5 rows selected.
I have a problem with views and nested selects which I cannot explain. Here is a trimed down version of the research I have done. notice the following:
1) all code is executed from the same user CDRNORMALCODE. this user has all views and procedural code
2) all data is owned by a different user CDRDATA. This user has no views and no code.
My problem is this:
If I reference the table directly with a delete statement that uses a nested select (i.e. IN clause with select), the index I expect and want is used.But if I execute the same delete but reference even the most simple of views (select * from <table>) instead of the table itself, then a full table scan is done of the table.
Here is an execute against the table directly (owned by cdrdata). Notice the reference to the table in the table schema on line 3. Also please notice INDEX RANGE SCAN BSNSS_CLSS_CASE_RULE_FK1 at the bottom of the plan.
SQL> show user
USER is "CDRNORMALCODE"
SQL>
SQL> explain plan for
2 delete
[code]...
OK, here is an update. The views I am useing normally have instead of triggers on them. If I remove the instead of trigger the problem looks like it goes away, when I put the trigger back the problem comes back.But why would an instead-of-trigger change the query plan for a view?
SQL> DELETE FROM PLAN_TABLE;
5 rows deleted.
SQL> explain plan for
2 delete
3 from BSNSS_CLSS_MNR_CASE_RULE_SV
[code]...
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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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Feb 11, 2011
Our application servers will be running a SELECT which returns zero rows all the time.This SELECT is put into a package and this package will be called by application servers very frequently which is causing unnecessary CPU.
Original query and plan
SQL> SELECT SEGMENT_JOB_ID, SEGMENT_SET_JOB_ID, SEGMENT_ID, TARGET_VERSION
FROM AIMUSER.SEGMENT_JOBS
WHERE SEGMENT_JOB_ID NOT IN
(SELECT SEGMENT_JOB_ID
FROM AIMUSER.SEGMENT_JOBS) 2 3 4 5 ;
[code]....
Which option will be better or do we have other options?They need to pass the column's with zero rows to a ref cursor.
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Sep 25, 2013
select
serialnumber from product where productid in
(select /*+ full parallel(producttask 16) */productid from producttask where
startedtimestamp > to_date('2013-07-04 00:00:00', 'YYYY-MM-DD HH24:MI:SS')
and startedtimestamp < to_date('2013-07-05 00:00:00', 'YYYY-MM-DD HH24:MI:SS')
and producttasktypeid in
[code]....
Explain plan output:
Plan hash value: 2779236890
-----------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name| Rows| Bytes | Cost (%CPU)| Time| Pstart| Pstop |
-----------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT || 1 | 29 | 9633M (8)|999:59:59 |||
|* 1 | FILTER |||| ||||
| 2 | PARTITION RANGE ALL || 738M| 19G| 6321K (1)| 21:04:17 | 1 | 6821 |
[code]....
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter( EXISTS (<not feasible>)
4 - filter("PRODUCTID"=:B1)
5 - filter(ROWNUM<100)
12 - access("MODELID"=:B1)
[code]....
Note: - SQL profile "SYS_SQLPROF_014153616b850002" used for this statement
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Nov 27, 2010
Using rownum in PL/SQL can significantly reduce performance and throughput of queries.
For example,
CODEselect *
from (select ...
from ...
join ... on ...
join ... on ...
left join ... on ...
where ...
group by ...)
where rownum < 500
takes much more time on a heavy loaded db than
CODEselect Y.*
from (
select X.*, rank() over(order by ...) rnk
from (select ...
from ...
join ... on ...
join ... on ...
left join ... on ...
where ...
group by ...) X) Y
where rnk < 500
I suspect it's because Oracle optimizer goals all_rows and first_rows.
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Apr 23, 2010
how to select 1st record from duplicate vales in a table.
If we created one table with out primary key column In form in search block have uwi value and top_depth value when i enter uwi and top_depth value then when i click search button then it will display all values in master block.
but here duplicate values r there.
SQL> select rownum,uwi,top_depth,base_depth,test_start_date from well_pre_header;
ROWNUM UWI TOP_DEPTH BASE_DEPTH TEST_STAR
---------- ---------------- ---------- ---------- ---------
1 100 453.05 458.08 09-SEP-10
2 100 200 288 23-AUG-00
3 1001 200 289 25-AUG-01
4 1001 200 201 24-MAY-87
if uwi = 1001 and top_depth=200 and i will click search button it should be display 3 record & when i click next button then it will show 4th record.
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Mar 3, 2011
I have a table with around 80 columns. All i need is to select first 40 columns.
Is there any way to select first 40 columns without giving all the 40 Column Names in select clause.
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Jun 26, 2010
I have a table that partitioned into six partitions. each partitions placed in different table space and every two table space placed it on a different hardisk
when I will do query select with the non-partition keys condition, how the search process ? whether the sequence (scan sequentially from partition 1 to partition 6) or partition in a hardisk is accessed at the same time with other partition in other hardisk. ( in the image, partition 1,4 accessed at the same time with partition 2,5 and 3,6)
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Jul 12, 2010
Looking to understand the difference between instance tuning and database tuning.
What is the difference between these two tuning exercises? I understand that an instance is memory based structures (logical) where as database consists of physical structures.
However, how does one tune a database the physical structure? Does it have to do with file placements/block sizes etc. Would you agree that a lot of that is taken care by ASM now in 11g? What tools are required/available (third party as well as oracle supplied) for these types of tuning scenarios?
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Oct 31, 2011
I have two tables with 113M records in DWH_BILL_DET & 103M in prd_rerate_chg_que and Im running following merge query, which is running for 13 hrs to update records, which is quiet longer time.
SQL> explain plan for MERGE /*+ parallel (rq, 16) */
INTO DWH_BILL_DET rq
USING (SELECT rated_que_rowid,
detail_rerate_flag_code,
rerate_sel_key,
[code].....
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Sep 30, 2010
How the length of column width effects index performance?
For example if i had IOT table emp_iot with columns:
(id number,
job varchar2(20),
time date,
plan number)
Table key consist of(id, job, time)
Column JOB has fixed list of distinct values ('ANALYST', 'NIGHT_WORKED', etc...).
What performance increase i could expect if in column "job" i would store not names but concrete numbers identifying job names.
For e.g. i would store "1" instead 'ANALYST' and "2" instead 'NIGHT_WORKED'.
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Jun 16, 2010
I have a question about database fragmentation.I know that fragmentation can reduce performance in query times. The blocks are distributed in many extents and scans process takes a long time. Oracle engine have to locate the address of the next extent..
I want to know if there is any system view in which you can check if your table or index has high fragmentation. If it's needed I will have to re-create, move or rebulid the table or index, but before I want to know if the degree of fragmentation is high.
Any useful script or query to do this, any interesting oracle system view?
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Oct 20, 2010
There is a simple way to increase the performance of a query by reducing the row-size of the table it hits. I used it in the past by dividing the table into smaller parts and querying respective smaller table in each query.
what is this method called ? just forgot the method and can't recall it. what this type of row-reduction optimization is called ?
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