where rownum < N is slow

Hi all

I'm on a 10.2.0.4 db SE CARS.

When I run

Select * from < table > where rownum < N

The application hangs as if the DBMS must have run a full scan of the table.

Do you have any idea why this is happening?

Thanks in advance

Tags: Database

Similar Questions

where rownum < 10 translated by fts

Hello
I have a table with 200 million indexed documents and I thought crawled correctly. If I SELECT field1 FROM large_table WHERE rownum < 10, it returns 9 entries in a few seconds. If I select * from large_table where rownum < 10, I get a full table scan. Can someone explain it to me please?
I'm under 11 GR 2, 4 blade cluster.
Thank you
Randy

execution plans tell us many things: in this case, we can see that you go to a partitioned table and that the optimizer uses a full index scan to produce the result for the first query. It is an option, because the v_reference_no column is included in the PKP_DBCR_T index and the optimizer decides to start playback of the structure of the comprehensive index with multiblock read operations to avoid access table completely - basically a systematic index scan full is very similar to a full table scan access the smallest segment index and not the table (even if it is not impossible that an index is greater than the) table but that's another story).

For the second query Oracle uses the full table scan, since it is not possible to read all the necessary information of the index - and the small cost and time values tell us that the optimizer expects that this operation is very cheap and fast. If is not, then this could be a consequence of the empty partition or almost empty with several blocks but a few existing lines: in this case, the engine must analyze many blocks before the stop condition (with the filter stopkey County< 10)="" is="" reached,="" the="" result="" is="" produced,="" and="" the="" scan="" can="" be="">

Rownum works only where rownum = 1

Hello
I have a query that will return the 2 rows:

SQL> select start_date
  2  from employees join job_history using (employee_id)
  3  where employee_id = 2168
  4  order by start_date desc;
 
START_DATE
-----------
01/04/2004
02/03/2003

I wanted to have the first line in this result, so I used rownum and it worked:

SQL> select x.start_date
  2       from (select start_date
  3             from employees join job_history using (employee_id)
  4             where employee_id = '2168'
  5             order by start_date desc) x -- the first row will be the latest start_date
  6       where rownum = 1;
 
START_DATE
-----------
01/04/2004

But when I wanted to get the number of line 2, it returns null:

SQL> select x.start_date
  2       from (select start_date
  3             from employees join job_history using (employee_id)
  4             where employee_id = '2168'
  5             order by start_date desc) x -- the first row will be the latest start_date
  6       where rownum = 2;
 
START_DATE
-----------

Why is this?
Thank you

Rownum is applied to the result that the records are returned. So the first record in the result set always has {make: courier new} rownum = 1 {font}. If {make: courier new} rownum = 2 {font} can never be true. This is a discussed [url http://docs.oracle.com/cd/B19306_01/server.102/b14200/pseudocolumns009.htm#i1006297] in the SQL manual.

It is an old chestnut and the solutions are easily detectable, but they all involve using a nested query to a description.

select * from
    ( select t.*, rownum as rn
      from your_table t
    )
where rn = 2;

To have a sorted result set you need two layers of nesting:

select * from
    ( select t.*, rownum as rn
      from
        (  select * your_table
          order by whatever
        ) t
    )
where rn = 2;

Cheers, APC

SELECT... where ROWNUM > 1 does not work?
Hi all

We are working to try to finally update some lines on a table that has an application processing threads.
We are essentially trying to update the value of a field, which he uses to 'mark' which belongs to this process.

During this operation, we have tried to reset this field on some lines above where he works. We tried to use rownum.

It did not work, then to try to resolve the problems... we tried just a select base to see if it returns all values to ensure that the rownum would work (don't know why it wouldn't).

If I try the following I get weird results

SELECT count (*) from table1.

Returns as 13000 lines for a charge.

I do this

SELECT count (*) from table1 where rownum > 1

I have no lines.

The table has 13000 lines inside...

Now, if I do something like a select col1 from table1 where rownum < 10.
I get 9 rows...

I'm intrigued by this...

This came initially to try to update as I said and he was trying to do something like:

Update table1 set Field1 = 'value' where rownum between 1000 and 3000.

No rows updated.

I have not played with rownum in a while, someone can give me an idea about what is happening here, or some links Info?

Thanks in advance,

Cayenne
Keep in mind, rownum pseudo-column query given the row number in the result of outpup.
I'll try to resume Oracle doing the test of rownum > 1:
1. based on your where clause, Oracle will retrieve a line, rownum = 1 (because it's the first row returned), test if it is > 1, it is not, then do not get this line, then rownum back to its previous value, 0
2 oracle gets another line, rownum = previous value (0) + 1 = 1 (because some lines have been returned yet), test if it is > 1, it is not, then don't you either this line, then rownum back to its previous value, 0
3 see point 2
4. Finally, no line is returned because rownum is still stuck on '0 '.

Nicolas.

Any problem with using WHERE ROWNUM = 1?
DB version: 10 gr 2

When you want to get a single row of a resultset, is there something wrong in using
```
 where rownum = 1
 
```
as in
```
 select ename,sal from emp where rownum=1
 
```
Nothing wrong but the result is the problem is not deterministic. use of ROWNUM = 1 do not guarantee the same output every time.

Rownum and plan to see where Explain the terms > and <

Hi people...
I just wanted to share a comment... would make for a conceptual explanation on even!
SQL > select * from v version $;
BANNER
-----------------------------------------------------------------------------
Database Oracle 12 c Enterprise Edition Release 12.1.0.1.0 - 64 bit Production
PL/SQL Release 12.1.0.1.0 - Production
CORE Production 12.1.0.1.0
AMT for 64-bit Windows: Version 12.1.0.1.0 - Production
NLSRTL Version 12.1.0.1.0 - Production
SQL > select count (*) in the tab_rownum where rownum < 2;
Execution plan
----------------------------------------------------------
Hash value of plan: 1301825293
--------------------------------------------------------------------------
| ID | Operation | Name | Lines | Cost (% CPU). Time |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT |            |     1.     2 (0) | 00:00:01 |
|   1. GLOBAL TRI |            |     1.            |          |
|* 2 |   COUNT STOPKEY |            |       |            |          |
|   3.    TABLE ACCESS FULL | TAB_ROWNUM |     1.     2 (0) | 00:00:01 |
--------------------------------------------------------------------------
Information of predicates (identified by the operation identity card):
---------------------------------------------------
2 - filter(ROWNUM<2)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block Gets
3 consistent gets
5 physical reads
0 redo size
542 bytes sent via SQL * Net to client
543 bytes received via SQL * Net from client
2 SQL * Net back and forth to and from the client
0 sorts (memory)
0 sorts (disk)
1 rows processed
As most of us should be aware of, First_Rows_k optimization takes place for query Rownum... !!
so for top query, the cardinality estimate is 1 and County stop happened key in the plan with filter as ROWNUM < 2.
Now let's run under SQL.
SQL > select count (*) in the tab_rownum where rownum > 2;
In any case... above SQL will be not all output lines.
As expected rownum is greater then 2... !!
allows to check the plan!
Execution plan
----------------------------------------------------------
Hash value of plan: 141762995
---------------------------------------------------------------------------
| ID | Operation | Name | Lines | Cost (% CPU). Time |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT |            |     1.   425 (1) | 00:00:01 |
|   1. GLOBAL TRI |            |     1.            |          |
|   2.   COUNTY |            |       |            |          |
|* 3 |    FILTER |            |       |            |          |
|   4.     TABLE ACCESS FULL | TAB_ROWNUM | 91740 |   425 (1) | 00:00:01 |
---------------------------------------------------------------------------
Information of predicates (identified by the operation identity card):
---------------------------------------------------
3 - filter(ROWNUM>2)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block Gets
1529 gets coherent
1526 physical reads
If we check the cardinality estimates, this is the total of the lines of the table... That's why no First_Rows_K for this SQL optimization. (All_rows)
Although we will not get all the lines... always full scan table oracle...
Also... Button Count Stop has changed and filter + Count... !!
Need to understand... Why not oracle have an output for logic > rownum conditions than zero!
Why the filter for the second execution ends not SQL executions... it scan complete set... for lines nil!
Thank you
Deepak M.

Hello

WHERE ROWNUM > 2 is a very common mistake, but it's a mistake that most people make once, in development. They learn that it does not work, and they don't again. I expect Oracle to make the features so that unique development queries run faster. They are probably more concerned about what kind of things people do every day, in the Production.

order by with rownum

Hi Hello all please help me I want to choose folder 100 100000 record Albums, but my answer to the query is too slow. Please give me an idea to improve this issue.
Select *.
from (SELECT *)
of dhcpactivitylogs
WHERE CREATEDDATE BETWEEN
18 NOVEMBER 14 1.00.00 AM'
AND
21 NOVEMBER 14 12.00.00 PM'
dhcpactivitylogsid desc order)
where rownum < = 100;

If im using simple rownum works it random return 100 and I need top 100.

If there are indexes on (DHCPACTIVITYLOGSID, CREATEDDATE) and the query is changed, a little bit like below, you should see "stop key" somewhere in the plan which comes only 100 lines in the order of the index.

Select *.

from (SELECT t.*, rownum rn

of dhcpactivitylogs t

WHERE CREATEDDATE BETWEEN

18 NOVEMBER 14 1.00.00 AM'

AND

21 NOVEMBER 14 12.00.00 PM'

dhcpactivitylogsid desc order)

-where rownum<=>

where rn<=>

SQL performance problem associated with rownum.

Dear Experts,
I have a sql
SELECT TEMP.col1, TEMP.col2, TEMP.col3, TEMP.col4, TEMP.col5, ROWNUM, not
(SELECT col1, col2, col3, col4 FROM table1 ORDER BY DESC col4 col5) TEMP WHERE rownum between? and?
When I put the value of range rownum 1 and 100, it works very well. But when I put 101 and 200 no records returned.
So I modified it as fllows
SELECT TEMP.col1, TEMP.col2, TEMP.col3, TEMP.col4, TEMP.col5,NWR No. OF
(SELECT col1, col2, col3, col4, col5, rownum NWR FROM table1 ORDER BY DESC col4) TEMP WHERE NWR between? and?
It works fine and giving results desire. But the issue here is the modified SQL becomes very slow. It gives results in 20 minutes. Although SQL earlier gave results in a few seconds.
Records in table1 is 40 million.
Is there another way to get good performance results accurate?
Your help will be much appreciated.
Kind regards
DD

Hi try this... If you want that data should be in the specific order (as order by desc col4, then you can use analytical ROW_NUMBER() function as below). Try it out below and let me know in case of any problems

SELECT TEMP.col1,

TEMP.col2,

TEMP.col3,

TEMP.col4,

TEMP.col5,

NWR NO.

FROM (SELECT col1,

col2,

col3,

COL4,

col5,

ROW_NUMBER() over (ORDER BY DESC of col4) rno

FROM table1)

NWR WHERE between 101 AND 200;

(GOLD)

SELECT TEMP.col1,

TEMP.col2,

TEMP.col3,

TEMP.col4,

TEMP.col5,

NWR NO.

FROM (SELECT col1,

col2,

col3,

COL4,

col5,

ROW_NUMBER() OVER(ORDER BY col4 DESC) NWR

FROM table1)

WHERE NWR<=>

"the db file sequential read" waiting for event slow down an application.

"the db file sequential read" waiting for event slow down an application.

It is a rather strange problem. There is an update statement that hangs on the wait event 'db file sequential read' and until you restart the database, the query works fine. It happens once a week, usually Monday or after several days of large amount of work.

I checked the processor and is fine, memory is very good, although the SGA and PGA have taken maximum memory. Flow of the disc seems to be ok since each another session on the basis of data looks very good.

I guess that there is a missing configuration to avoid having to restart the database each week.

Any help is greatly appreciated.

Hello

If you want same order of the tables as plain exp after reboot just go with ordered hint

UPDATE item_work_step
SET user_name = :b1,
terminal = SYS_CONTEXT ('USERENV', 'TERMINAL'),
status_cd = 'IN PROCESS'
WHERE item_work_step_route_id =
(SELECT item_work_step_route_id
FROM (SELECT /*+ORDERED */ iws.item_work_step_route_id
FROM user_role ur,
work_step_role wsr,
work_step ws,
app_step aps,
item_work_step iws,
item_work iw,
item i
WHERE wsr.role_cd = ur.role_cd
AND ws.work_step_id = wsr.work_step_id
AND aps.step_cd = ws.step_cd
AND iws.work_step_id = ws.work_step_id
AND iws.work_id = ws.work_id
AND iws.step_cd = ws.step_cd
AND iws.status_cd = 'READY'
AND iw.item_work_id = iws.item_work_id
AND iw.item_id = iws.item_id
AND iw.work_id = iws.work_id
AND i.item_id = iws.item_id
AND i.item_id = iw.item_id
AND i.deleted = 'N'
AND i.item_type_master_cd = :b3
AND ur.user_name = :b1
AND aps.app_name = :b2
AND ( iws.assignment_user_or_role IS NULL
OR ( iws.assignment_user_or_role IN (
SELECT ur.role_cd
FROM user_role ur
WHERE ur.user_name = :b1
UNION ALL
SELECT :b1
FROM dual)
AND iws.assignment_expiration_time > SYSDATE
)
OR ( iws.assignment_user_or_role IS NOT NULL
AND iws.assignment_expiration_time <= SYSDATE
)
)
AND (iws.pend_date IS NULL OR iws.pend_date <= SYSDATE
)
ORDER BY aps.priority,
LEAST (NVL (iw.priority, 9999),
NVL ((SELECT NVL (priority, 9999)
FROM item_work
WHERE item_id = i.parent_id
AND work_id = 42),
9999
)
),
DECODE (i.a3, NULL, 0, 1),
NVL (iw.sla_deadline,
(SELECT sla_deadline
FROM item_work
WHERE item_id = i.parent_id
AND work_id = 42)
),
i.parent_id,
i.item_id) unclaimed_item_work_step
WHERE ROWNUM <= 1)

If you want to get rid of the nested loops use USE_HASH

UPDATE item_work_step
SET user_name = :b1,
terminal = SYS_CONTEXT ('USERENV', 'TERMINAL'),
status_cd = 'IN PROCESS'
WHERE item_work_step_route_id =
(SELECT item_work_step_route_id
FROM (SELECT /*+ORDERED USE_HASH(ur wsr ws aps iws iw i) */ iws.item_work_step_route_id
FROM user_role ur,
work_step_role wsr,
work_step ws,
app_step aps,
item_work_step iws,
item_work iw,
item i
WHERE wsr.role_cd = ur.role_cd
AND ws.work_step_id = wsr.work_step_id
AND aps.step_cd = ws.step_cd
AND iws.work_step_id = ws.work_step_id
AND iws.work_id = ws.work_id
AND iws.step_cd = ws.step_cd
AND iws.status_cd = 'READY'
AND iw.item_work_id = iws.item_work_id
AND iw.item_id = iws.item_id
AND iw.work_id = iws.work_id
AND i.item_id = iws.item_id
AND i.item_id = iw.item_id
AND i.deleted = 'N'
AND i.item_type_master_cd = :b3
AND ur.user_name = :b1
AND aps.app_name = :b2
AND ( iws.assignment_user_or_role IS NULL
OR ( iws.assignment_user_or_role IN (
SELECT ur.role_cd
FROM user_role ur
WHERE ur.user_name = :b1
UNION ALL
SELECT :b1
FROM dual)
AND iws.assignment_expiration_time > SYSDATE
)
OR ( iws.assignment_user_or_role IS NOT NULL
AND iws.assignment_expiration_time <= SYSDATE
)
)
AND (iws.pend_date IS NULL OR iws.pend_date <= SYSDATE
)
ORDER BY aps.priority,
LEAST (NVL (iw.priority, 9999),
NVL ((SELECT NVL (priority, 9999)
FROM item_work
WHERE item_id = i.parent_id
AND work_id = 42),
9999
)
),
DECODE (i.a3, NULL, 0, 1),
NVL (iw.sla_deadline,
(SELECT sla_deadline
FROM item_work
WHERE item_id = i.parent_id
AND work_id = 42)
),
i.parent_id,
i.item_id) unclaimed_item_work_step
WHERE ROWNUM <= 1)

and for small tables, you can try adding for example FULL (your) FULL (wsr)

It can be rewritten in a different way, but it's the fastest way to try how query will be if you rewrite it. Check the explain plan command if certain partially ordered tables are not joined because you can get the Cartesian join, it seems that it will be ok.

View query result in the em console.

Concerning

New laptop is slow

laptop HP pavilion 15-p010us touchsmart, 2.4 GHz amd quad-core a8-6410 apu

My laptop is fairly new, almost a week. It was perfectly fine the first day but then I noticed cela lag and take some time to open anything, is it it open to all. For example, several times I would try opening Google Chrome and it loads but then act as ever, I clicked it or I want to click on something and I would get no reaction until a few minutes later, when its action. Ive updated the necessary updates and recommended to try to solve the problem, but it continues to lag. It takes forever to open a new page. It loads to a blank screen for a minute and then go to the page I wanted. I checked my network via Xfinity speed Checker speed and the results were normal, according to them. I would really help because it is really new and I don't understand why I'm constantly waiting for the simplest of things to open or load. Ive done complete analyses with nothing detected and my pc is protected. I bought a new laptop because my old one was too slow I have not downloaded or installed anything before that happens outside of Google Chrome

Edit: Ive searched around the internet and found similar problems where McAfee is actually slow down the computer and uninstall helped. That would help? What is the best protection for computers that are not slow it down?

Hello

Thanks for posting in the Forum of Support HP!

Yes, McAfee can slow some computers and could cause performace issues such as you describe.

S ' Please, uninstall it in Panel of-> programs and features

-Restart the computer

-Check >this article and download the McAfee consumer product removal tool

-Restart the computer

Test now and confirm if the issue is resolved.

Some additional tips you could read >here

You can also download and run CCleaner (Slim edition) free edition

In regard to your question fast, light and effecent AV/malware protection, I personally recommend that you try ESET NOD32 or ESET Smart Security www.eset.com

Please, post again and I would like to know the results. Happy holidays!

T430 is very slow after fashion 'sleep'

I have a T430 is a couple of months. I had this problem from the beginning. Care clean (have a Dell laptop with the same characteristics and there never have this issue).

Processor: Intel Core i5 - 3320 M CPU @ 2.60 GHz

RAM: 4 GB

Basically after each time the laptop is in mode "standby" for more than 30 minutes, once I open the laptop and connect, there is a period of 3 to 4 minutes where it is EXTREMELY slow. The computer train ridiculously.

No idea why this may be?

Hey Gradstud40,

I think you'd find this useful knowledge base Article . He wrote to another machine for a slow start, however the steps will be useful for better functionality to your computer as a whole and should speed up your computer when returning from standby mode.

Extremely slow laptop

Hi, I have a Dell Laptop Inspiron 1300 I use in the store where I work. He got to the place where is is extremely slow to start, open a browser and sometimes even locksup.

I went to the Dell view and ran the full derniŠre utility and everything happened but the 'line read test '. When the desired content 'read the line' he would say "running" but would never be progess is omitted or passed. " I then tested the HD only. There are two tests. Test the HD and HD stress test. The HD passed the test of the HD, but when I run the test of stress of HD and he looked at the line 'reading' the same test as above has happened.

I guess that the HD is bad and he is about to die.

Any thoughts on this would be appreciated.

Thanks for your help. Problem solved. Compensation settled and it fixed the problem. I'm confused by the slow start. But live and learn.

Thanks again.

Rownum and order of columns not indexed

Why ROWNUM continue to take the same cost?

Why can't you see no difference between the ORDER of SORTING BY STOPKEY and just SORT ORDER BY?

SQL_ID, 9vccbf2dtazuq, number of children 0

-------------------------------------

Select * from (select * from PROCESS_MESSAGE by id) where

rownum < 101

Hash value of plan: 2507589572

------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | | | | 1252K (100) | |

|* 1 | COUNT STOPKEY | | | | | | |

| 2. VIEW | | 26 M | 40G | | 1252K (1) | 00:00:49 |

|* 3 | SORT BY STOPKEY ORDER. | 26 M | 4736M | 5835M | 1252K (1) | 00:00:49 |

| 4. TABLE ACCESS FULL | PROCESS_MESSAGE | 26 M | 4736M | | 170K (1) | 00:00:07 |

------------------------------------------------------------------------------------------------------

Information of predicates (identified by the operation identity card):

---------------------------------------------------

1 - filter(ROWNUM<101)

3 - filter(ROWNUM<101)

SQL_ID, 2zwdanc062902, number of children 0

-------------------------------------

Select * from PROCESS_MESSAGE by id

Hash value of plan: 1046773234

-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | | | | 1252K (100) | |

| 1. SORT ORDER BY | | 26 M | 4736M | 5835M | 1252K (1) | 00:00:49 |

| 2. TABLE ACCESS FULL | PROCESS_MESSAGE | 26 M | 4736M | | 170K (1) | 00:00:07 |

-------------------------------------------------------------------------------------------------

Cost is not something that I want to live. Here's a simple example. Search for the-row, A-Time and memory usage for the SORT operation on both the query to see the difference.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> create table t as
  2  select rpad ('x', 1000, 'x') str from dual
  3  connect by level <= 10000;

Table created.

SQL> exec dbms_stats.gather_table_stats(user, 'T')

PL/SQL procedure successfully completed.

SQL> alter session set statistics_level = all
  2  ;

Session altered.

SQL> @temp.txt

PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  c4qj1q3h9kkyy, child number 0
-------------------------------------
select * from t order by str

Plan hash value: 3672837129
--------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation          | Name | Starts | E-Rows |E-Bytes|E-Temp | Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |
--------------------------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |      1 |        |       |       |  2018 (100)|          |  10000 |00:00:00.25 |    1433 |       |       |          |
|   1 |  SORT ORDER BY     |      |      1 |  10000 |  9775K|     9M|  2018   (1)| 00:00:20 |  10000 |00:00:00.25 |    1433 |    11M|  1285K|    9M (0)|
|   2 |   TABLE ACCESS FULL| T    |      1 |  10000 |  9775K|       |   225   (1)| 00:00:03 |  10000 |00:00:00.02 |    1433 |       |       |          |
--------------------------------------------------------------------------------------------------------------------------------------------------------

14 rows selected.

PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  8a53npuzuxxj5, child number 0
-------------------------------------
select * from (select * from t order by str) where rownum <= 50

Plan hash value: 1317717595
-------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation               | Name | Starts | E-Rows |E-Bytes|E-Temp | Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |
-------------------------------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT        |      |      1 |        |       |       |  2018 (100)|          |     50 |00:00:00.08 |    1433 |       |       |          |
|*  1 |  COUNT STOPKEY          |      |      1 |        |       |       |            |          |     50 |00:00:00.08 |    1433 |       |       |          |
|   2 |   VIEW                  |      |      1 |  10000 |  4902K|       |  2018   (1)| 00:00:20 |     50 |00:00:00.08 |    1433 |       |       |          |
|*  3 |    SORT ORDER BY STOPKEY|      |      1 |  10000 |  9775K|     9M|  2018   (1)| 00:00:20 |     50 |00:00:00.08 |    1433 | 61440 | 61440 |55296  (0)|
|   4 |     TABLE ACCESS FULL   | T    |      1 |  10000 |  9775K|       |   225   (1)| 00:00:03 |  10000 |00:00:00.01 |    1433 |       |       |          |
-------------------------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter(ROWNUM<=50)
   3 - filter(ROWNUM<=50)

22 rows selected.

Edited...

Looking for more, if you see the lines-E in the second request its 10000 for SORTING display. But the row that is the true value is 50. Maybe this could be a factor why the cost of both the request are the same.

rownum

Hi all

I use

Connected to Oracle Database 11g Express Edition Release 11.2.0.2.0

I use the Oracle HR schema

I'm learning the rownum with order of

In the two order statement is in even

but a 2nd has ROWNUM < 6

The result set is different

Please help me understand the problem

SQL > SELECT LAST_NAME, HIRE_DATE

2 EMPLOYEES

3 ORDER OF HIRE_DATE

LAST_NAME HIRE_DATE

------------------------- -----------

De Haan 13/01/2001

Gietz 06/07/2002

Baer 06/07/2002

Mavris 06/07/2002

Higgins 07/06/2002

Faviet 16/08/2002

SQL > SELECT LAST_NAME, HIRE_DATE

2 EMPLOYEES

3. WHERE ROWNUM < 6

4 ORDER OF HIRE_DATE

LAST_NAME HIRE_DATE

------------------------- -----------

De Haan 13/01/2001

King 17/06/2003

Kochhar 21/09/2005

Hunold 03/01/2006

Ernst 21/05/2007

Thank you

Hello

second one you 5 random * (in theory at least) the lines you sort. If you need to sort the rows and get top 5 can do sorting in inline mode and which filter with rownum<>

-- without ordering 5 rows
SELECT LAST_NAME,HIRE_DATE
FROM EMPLOYEES
WHERE ROWNUM < 6
;
-- order those 5 rows
SELECT LAST_NAME,HIRE_DATE
FROM EMPLOYEES
WHERE ROWNUM < 6
ORDER BY HIRE_DATE
;
-- select all employees, sort them and then return top 5 of them
SELECT * FROM (
  SELECT LAST_NAME,HIRE_DATE
  FROM EMPLOYEES
  ORDER BY HIRE_DATE
)
WHERE ROWNUM < 6
;

LAST_NAME                 HIRE_DATE
------------------------- ----------
King                      17.06.2003
Kochhar                   21.09.2005
De Haan                   13.01.2001
Hunold                    03.01.2006
Ernst                     21.05.2007 

LAST_NAME                 HIRE_DATE
------------------------- ----------
De Haan                   13.01.2001
King                      17.06.2003
Kochhar                   21.09.2005
Hunold                    03.01.2006
Ernst                     21.05.2007 

LAST_NAME                 HIRE_DATE
------------------------- ----------
De Haan                   13.01.2001
Mavris                    07.06.2002
Gietz                     07.06.2002
Higgins                   07.06.2002
Baer                      07.06.2002

* randomly in this context means that there is no particular order what rows is returned. If the query is repeated, it seems that the lines in the same order each time, but this could change when data is modified in the table.

Using ROWNUM with SEQUENCE. NEXTVAL in the select statement

I have a table emp
SQL > select * from emp;
EMPNO, ENAME
---------- ----------
JOHN 5000
5001 ADAM
MIKE 5002
I need help to write a procedure to run ' select EMPNO | ENAME from emp' on a line at a time until the end of the table.
Try to use the below stated by "N as a sequence.nextval. It does not work. Please help me solve this.
Select EMPNO | ENAME from EMP
where rownum < N + 1
less
Select EMPNO | ENAME from EMP
where rownum < N;

So why not just make something like:

SQL > select "mysql - host = localhost - user = roor - password = rootpassword e ' create database ' |" " EmpNo | Ename | " » ;"
2 EMP;

"MYSQL - HOST = LOCALHOST - USER = ROOR - PASSWORD = ROOTPASSWORD-E" CREATEDATABASE'| "" EMPNO | ENAME | " » ;"
-------------------------------------------------------------------------------------------------------------------
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7369SMITH database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7499ALLEN database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7521WARD database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7566JONES database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7654MARTIN database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7698BLAKE database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7782CLARK database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7788SCOTT database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7839KING database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7844TURNER database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7876ADAMS database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7900JAMES database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7902FORD database';
MySQL--host = localhost - user = roor - password = rootpassword EI 'create the 7934MILLER database';

14 selected lines.

SQL >

Then, you can copy and paste the results in a script file and run this script.

Don't know why you want to wait 15 seconds between each, as the mysql command is not likely to return control to the script until it has finished creating the database (at least that's what would make most of the commands, I use MySQL)

where rownum &lt; N is slow

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