Which is faster; Count (1) or count (*)?

Similar Questions

• ETG vs. insert add in parallel (which is faster)?

  Hi all
  
  The oracle is 11.2.0.3 on a linux machine.
  
  I would like to know what the most rapid between the ETG and insert add in parallel (not index).
  
  ----------------
  
  case A: ETG
  
  create table table_a nologging Parallels 32
  as
  Select / * + full (t) parallel (32 t) * / *.
  of table_b t;
  
  case B: table_a was established in nologgig mode without index.
  
  Insert / * + full (t) parallel (32 t) * / into table_a
  Select / * + full (b) parallel (32B) * / *.
  of table_b b;
  
  -----------------------
  
  As far as I know, both use "direct path write."
  According to my experience, both show similar performance.
  
  I would like to hear your experience which is faster in general and in THEORY.
  
  Thanks in advance.
  Best regards.

  >
  I would like to know what the most rapid between the ETG and insert add in parallel (not index).
  . . .
  in my test case, the two sql show similar performance.
  >
  How do you know? You don't post any case INSERT ADD then why don't test you what you posted and we seek clarification?

• Which is faster or =

  Hello
  
  There are millions of records from a table and have to perform multiple filtering on the same column, which is faster
  
  table.column_name = 10
  or
  table.column_name = 20
  or
  table.column_name = 30
  or
  table.column_name = 40
  
  or+_
  
  table.column_name in (10,20,30,40)
  
  Thank you
  Vijay
  
  Published by: jvjmohan on January 11, 2011 02:42

  Hello

  There is so much difference in the two operators. in the case AND the requirements of thre must pass, only then you will get the output and there a lot of conditions

  In operator, it will not compare an object to another... What ever is in the requirement, it will give the result.

  IN operator within complexity... it will be faster.

• Initialize controls/indicators: invoke node-local variables Vales. Which is faster?

  Hi all

  I would like to get the opinion of the people. This thought just happened for me while I was reading some materials the other day.

  And I have not found any topic which talks specifically about speed after searching the forum.

  It is faster to initialize your controls/indicators using Invoke node OR write directly to the initial value of your local variables?

  From my experience (not large), I have always used the invoke node to initialize controls or indicators.

  But when I but this question, I did a simple reference point and it seems the local variable approach is faster, especially

  If you have the large number of orders/lights to initialize.

  Am I missing something here? The invoke node running something that writing a value of local variable would not do?

  I thought since you need to set the initial state by default for the node to invoke anyway, why not just write the desired initial value

  your local variables?

  I would appreciate if someone can express his own opinion based on their experience and knowledge.

  Thank you ~ ~

  I may need another Cup of coffee this morning, you are in fact callling the reset by default on each individual control.  My last despises, it is that you use the default method Vals.Reinitialize VI all failing.  It will probably be a bit faster than the method on individual controls.  Still not instant, if.

  Are a few msec is worth to you?  If so and you consider the local path, my advice is to group as many controls as possible into clusters for minimize you headaches.

• Which is faster a bit manipulation to the table or image using the vision

  I have to perform an operation on an image.  It involves the calculation of the new locations for the pixels for each pixel of the image.  Which is the fastest way to do it.  Manipulate the pixels as elements of the array for loops, or manipulate the pixels of an image using vision tools?

  Thank you.

  Hello

  If you can use vision tools to make the manipulation of pixels, it is much faster.

  Vladimir

• Which is faster - IN or EXISTS?

  Hello
  
  I have a small doubt... Please advise me... !!
  
  Exist is more IN more rapid because IN does not use the index at the time of the recovery but Exist uses Index at the time of extraction.
  
  
  My question is... If there is no index on the table... then there is what will do? that time is faster IN or Exists?
  
  see you soon
  Prabhu

  I'm not sure I understand your last post. If you want to "specific information", which sounds like you want to have a reasonable understanding detailed how Oracle manages the two different buildings, and when one might be preferred over the other. If you don't want 'bulky info', however, which makes it sound like you don't want details. So I'm a bit confused.

  If you don't want details, the answer is "it depends." For a given query, either IN or EXISTS may be more effective or that there may be no difference. In general, if the outer query returns a large number of lines and the inner query returns a small number of lines, IN would be probably more effective. If the outer query returns a small number of lines and the inner query returns a large number of lines, EXISTS would probably be more effective. In addition, it is potentially to try all variations and examine query plans if you are particularly concerned about performance.

  If you don't want details, read discussions of Tom.

  Justin

• NiMax tasks vs tasks created in the code which is faster?

  I'm curious as to which is better to use, tasks created in NiMax or tasks created in the code? If I acquire 8 analog channels, there is a downside to create tasks in NiMax speed? I know there is less code involved but what about the time it takes for labview read the configuration file that contains the tasks that are defined in NiMax? There is a significant advantage in the code?

  Thank you

  Bryan

  BryanSw wrote:

  I'm curious as to which is better to use, tasks created in NiMax or tasks created in the code? If I acquire 8 analog channels, there is a downside to create tasks in NiMax speed? I know there is less code involved but what about the time it takes for labview read the configuration file that contains the tasks that are defined in NiMax? There is a significant advantage in the code?

  Thank you

  Bryan

  I'd go with the third Option (which is the one I use) - set the task in the project.  First of all, define the task in MAX, make sure it does what you want and you are happy with it.  Then go into project, New, DAQmx task, and once again, to register in the project.  Use one in the project, which "lives" with the project and not with MAX.  If you need to change a parameter at run time, it is a great time to get some code...

  Bob Schor

• HotSync: Bluetooth or cable - which is faster

  I wonder if there is a significant difference between Bluetooth and cable in terms of speed of synchronization. I have a Vista (Palm Desktop 6.2.2) with Centro. Blutooth seems convinient since no physical link between Centro and my PC is necessary. But I want the synchronization time could be shorter. Would it be shroter if I used the physical cable connection?

  Cable clocks are certainly faster than bluetooth synchronization. You can always watch where your device is hung up the bluetooth synchronization. For example, once a month, I'll do a sync cable that I call a full synchronization. When I do synchronizations bluetooth I disable backup and disable media and just let my pim data sync and I don't see a significant difference.

  Message relates to: Centro (Sprint)

• Which is faster in performance

  Hi all
  
  I have a partition on the table according to the 5 data sources, i.e. the partition list. Table has about 100 KB of data.
  
  gives better performance?
  
  Select * from tab1 where source = 2;
  
  or
  
  Select * from tab1 partition (sr2);
  
  Please suggest. As I need to use in queries using several of these tables.
  
  Thank you
  VJ

  jvjmohan wrote:

  I have a partition on the table according to the 5 data sources, i.e. the partition list. Table has about 100 KB of data.
  gives better performance?
  Select * from tab1 where source = 2;
  or
  Select * from tab1 partition (sr2);

  Both are the same - a FTS of the contents of a single partition (assuming I read your comparison properly).

  The problem with the 2nd approach is that uses a static reference to the partition. This cannot be a binding parameter. So let's say you have a 100 sheet music - there will be a 100 sliders in the shared pool for research as follows:
  Select * from tab1 partition (sr1)
  Select * from tab1 partition (sr2)
  ..
  Select * from tab1 partition (sr100)

  This is problematic. In PL/SQL (or), this means having to use dynamic SQL to create an SQL statement with the reference to the correct partition.

  If the criteria of the partition is used, a single SQL cursor is necessary in the shared pool:
  Select * from tab1 where source =: 1

  And this slider can be used for all partitions of the table - as the value bound to the variable in the cursor, allows CBO to determine which partition to use (called partition size).

  In General - by specifying a name of partition in the SQL query is incorrect. Lack of technique use perspective. And also bad from a data modeling perspective. Application code does give not record the database indexes to use for a selectSQL names. So why and then specify the name of a partition in a SQL Select ?

  Inner layer of abstraction between database objects (indexes, partitions, constraints, etc.) and application SQL code, keep intact.

• Which is faster?

  I have a scénarion where I received a comment to replace the sliders of the Varray
  
  Who is the fastest between the slider and VArray? and why?

  What you have shown with this pseudo-code is a process loop nested within PL/SQL.

  In SQL, this is called a nested loops join. A loop through the primary table (external) and for each row in this table, hit the secondary table (inside).

  So, if the loop of the outer table has a 1000 lines, it means an iterations of the loop of 1000. For each iteration, it means release of another cursor on the secondary table - essentially running a 1000 SQL selects on this internal table.

  This is not suitable. Even if that SQL Select intern takes only a 100ms, each row of the outer table means that another 100ms is added to the total operating time. So performance wise, this structure is only a sensible approach when the outer loop table translates into a limited number of lines and therefore a limited number of iterations of the loop and a limited number of select on the inner table.

  The problem you have is therefore not a problem of the use of the wrong structure coding as do not use VARRAYs (never forget the fact that a VARRAY and a cursor are totally different things).

  The problem you have is a design problem. This approach to data processing through nested loops IS slow and IMPOSSIBLE to scale.

  This is why the SQL engine uses not only the treatment of nested loop. It also has the transformation of hash join, merge join transformation and a bunch of other sophisticated algorithms.

  And it is also why it is best to NOT code in PL/SQL nested loops, because the SQL engine has more algorithms in its arsenal to address this problem using a primitive nested loop.

  The design approach you should consider must be based SQL. For example

  // condition 1
  open cursor for
  select
    *
  from outer_table,
       inner_table1  // inner table for condition 1 data
  where outer_table.columns meet condition 1  // apply condition 1
  and outer_table.columns equals inner_table1.colums // join data
  
  // condition 2
  open cursor for
  select
    *
  from outer_table,
       inner_table2 // inner table for condition 1 data
  where outer_table.columns meet condition 2  // apply condition 2
  and outer_table.columns equals inner_table2.colums // join data
  
  etc.
  

• SELECT count VS table1 (column1) select count (*) from table1

  SELECT count VS table1 (column1) select count (*) from table1
  Which is faster, or are they equal in the aspect of the effectiveness and the cost of memory?

  Hello
  Reading this thread Øvre Asktom. You do not need to read anything except this, that would be perfectly answer to your question.
  http://asktom.Oracle.com/pls/asktom/f?p=100:11:P11_QUESTION_ID:1156159920245
  HTH
  Aman...

• Create a virtual channel that increases a counter for each iteration of a cyclic load test

  We will be a long period of cyclic fatigue tests, and I wish I could keep track of which iteration we are on this block.  The current plan is to test for 10 hours at 15 Hz, and then stop test for 2 hours for an inspection of the structure.  Later tests will begin upward.  Each of these blocks of 10 hours can start at a number of 0, but I would like to follow the release of our cell so that when he sees a rising edge (with filtering to take account of any noise) it will increase a 1 meter.  Each sample will then save this number in a column in the data file.  It doesn't have to be perfect in the measurement on the forehead, he sees the new cycle, but there need to be specific in the way that it is not miss or as an additional cycle.

  Is something like this in Signal Express full?

  Yes, what you are proposing is possible with SignalExpress full. You can call LabVIEW signal express code, so call a LabVIEW VI, which contains your counter code is a way to do it. If want to do entirely in SignalExpress you can use DAQmx features by browsing up to add a step > acquire signals > DAQmx acquire and put in place a task entry counter to match your needs.

• Do another counter for usb-6008 VI using Labview 8.5

  I want to create another counter for usb-6008 using Labview 8.5, it is necessary to calculate the two gears simultaneously.

  The best way to proceed is to use the meter.  The counter counts
  signals without having to interrupt the system or use the USB bus.
  When you ask the number of ticks that saw the meter, one
  request is thrown from the CPU to the USB line to the 6008, which then
  request counter "ticks how have you seen?  This number is
  returned on the USB bus, goes to the CPU and display on your
  screen.  Given that the DIO lines on the 6008 are software timed, it is
  no way to guarantee that the data back to the central unit is
  deterministic.  The conceptual difference between software-controlled
  DIO (that nondeterministically returns an entire stream) and a
  meter software-tick-application-controlled (which returns a unique number
  with the number of ticks) prevents us from using the DIO lines on the
  6008. the best way to count more edges is buying more 6008 s.
  Another possibility would be to buy a PCI card to counter such as
  the PCI-6602, who owns 8 counters. Most of the counters we offer in the
  USB form factor is 2 per device.

• increase the counter timebase pcie 6259

  Hello

  Im trying to perform 2 two edge measures 2 TTL signals separation using pcie 6259. I get an error msg 200140 ' 2 active edges consecutive input signals occurred without an edge timebase counter. " Use a faster counter time base. Ive tried to change the basis of counter time through the DAQmx channel nodes but my card is limited to a mx of 80 Mhz.

  Are there ways around that?

  concerning

  Don

  Hi the polar bear,

  Ive tried steve's idea to generate the PWM and it feeds my ctr and it works fine. If the problem was with my coupled signal with voltage comparator... you think you genius!

  Thanks heaps for your help.

  Don

• selection of special days and counting

  Hi all
  I need to select certain dates and the following days with the same criteria.
  An example would be:
  
  CREATE TABLE DEMO
  (
  EMP_ID NUMBER NOT NULL,
  WORKING_DAY DATE NOT NULL,
  ACTIVE_CODE NULL VARCHAR2 (1).
  CONSTRAINT DEMO_PK
  KEY ELEMENTARY SCHOOL (EMP_ID, WORKING_DAY)
  USING INDEX
  )
  
  
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('01.11.2010 00:00:00 '), '_');
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('02.11.2010 00:00:00 '), '_');
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('03.11.2010 00:00:00 '), 'K');
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('04.11.2010 00:00:00 '), 'K');
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('05.11.2010 00:00:00 '), 'K');
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('06.11.2010 00:00:00 '), NULL);
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('07.11.2010 00:00:00 '), NULL);
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('08.11.2010 00:00:00 '), 'K');
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('09.11.2010 00:00:00 '), '_');
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('10.11.2010 00:00:00 '), 'K');
  INSERT INTO DEMO (EMP_ID, WORKING_DAY, ACTIVE_CODE) VALUES (123, TO_DATE ('11.11.2010 00:00:00 '), '_');
  
  Now, I'm looking for the first day with Active_Code = 'K' and count the days that have 'K', too.
  Expected result: November 3-> 4 Ks (because the 8 is after the weekend); 10 November-> 1 K
  
  I hope that the example/explanation is not too bad...
  
  I built a procedure which was to count the occurrences, if I give the first occurrence (here the 3rd and 8th).
  But findign the first 'K' is my problem.
  A solution would be:
  AND
  (SELECT T2. T2 DEMO ACTIVE_CODE
  WHERE T2. EMP_ID = T1. EMP_ID AND T2. WORKING_DAY = T1. WORKING_DAY-1) <>'K '.
  AND
  (SELECT T2. T2 DEMO ACTIVE_CODE
  WHERE T2. EMP_ID = T1. EMP_ID AND T2. WORKING_DAY = T1. WORKING_DAY-2) <>'K '.
  AND
  (SELECT T2. T2 DEMO ACTIVE_CODE
  WHERE T2. EMP_ID = T1. EMP_ID AND T2. WORKING_DAY = T1. WORKING_DAY-3) <>'K '.
  
  But it is pretty darn imperformant if I'm dealing with millions of records :-(
  
  Could someone please give me a hint on how to solve this problem?
  Thank you.
  
  Best regards
  Christian

  Hi, Christian,.

  Assumiung you have exactly one line for each working_day (where active_code is not NULL):

  WITH     got_grp_num     AS
  (
       SELECT     emp_id
       ,     working_day
       ,     active_code
       ,       ROW_NUMBER ()
                    OVER ( PARTITION BY  emp_id
                        ORDER BY          working_day
                      )
             - COUNT ( CASE
                     WHEN  active_code = 'K'
                     THEN  1
                 END
                  )     OVER ( PARTITION BY  emp_id
                        ORDER BY          working_day
                      )      AS grp_num
       FROM     demo
       WHERE     active_code     IS NOT NULL
  --     AND     ...     -- Any filtering goes here
  )
  SELECT       emp_id
  ,       MIN (working_day)     AS first_day
  ,       COUNT (*)          AS cnt
  FROM       got_grp_num
  WHERE       active_code     = 'K'
  GROUP BY  emp_id
  ,       grp_num
  ORDER BY  emp_id
  ,         first_day
  ;
  

  I'm guessing on the emp_id role in this problem.

  The trickiest part of this problem is to obtain an appropriate value for the GROUP BY.
  When you have several consecutive lines of 'K', the difference between the ROW_NUMBER (in cash lines no 'K', but not weekends) and the number of lines of 'K' previous will be constant. This is what grp_num is. (A non - adjacent lines 'K' also has the same grp_num, but that's OK, it will be rejected by the WHERE clause in the main query.)

  Published by: Frank Kulash, November 4, 2010 05:43