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• Sqlite3 activerecord :order => "time DESC" doesn't sort

  - by Ole Morten Amundsen

  rails 2.3.4, sqlite3 I'm trying this Production.find(:all, :conditions = ["time ?", start_time.utc], :order = "time DESC", :limit = 100) The condition works perfectly, but I'm having problems with the :order = time DESC. By chance, I discovered that it worked at Heroku (testing with heroku console), which runs PostgreSQL. However, locally, using sqlite3, new entries will be sorted after old ones, no matter what I set time to. Like this (output has been manually stripped): second entry is new: Production id: 2053939460, time: "2010-04-24 23:00:04", created_at: "2010-04-24 23:00:05" Production id: 2053939532, time: "2010-04-25 10:00:00", created_at: "2010-04-27 05:58:30" Production id: 2053939461, time: "2010-04-25 00:00:04", created_at: "2010-04-25 00:00:04" Production id: 2053939463, time: "2010-04-25 01:00:04", created_at: "2010-04-25 01:00:04" Seems like it sorts on the primary key, id, not time. Note that the query works fine on heroku, returning a correctly ordered list! I like sqlite, it's so KISS, I hope you can help me... Any suggestions?

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• Java Caching on distributed environment

  - by Naren

  Hi, I am supposed to create a simple replicated cache using java for internal purpose which will be used in a distributed environment. I have seen oracle has implemented Replicated Cache Service. http://wiki.tangosol.com/display/COH32UG/Replicated+Cache+Service The problem I am facing is while doing an update or remove, I acquire lock on other cache's to the point the cache get's updated and notifies others of the change. This is eventually going into a dead lock situation, while removing. Is there any strategy I should follow while updating or removing from cache's. Can I implement a replicated cache without having a primary cache?? Thanks, Naren

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• Question about mysql indexes on low to medium cardinality columns

  - by Kevin J

  I have a general question about the way that database indexing works, particularly in mysql. Let's say I have a table with a million rows with a column "ClientID" that is distributed relatively equally among 30 values. Thus, this column is very low cardinality (30) relative to the primary key (1 million). Now, I understand that you shouldn't create indexes on low cardinality fields. However, in this case, queries are only ever done with one of the 30 clientIDs. Thus, wouldn't creating an index on ClientID be helpful, as the search space is automatically reduced to 1/30th what it normally would be? Or is my understanding of how the index works flawed? Thanks

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• Is there a way to retrieve the Computer Name of a Xenapp client?

  - by mlusby

  What options exist for identifying the client name of a particular client from within the process running on Citrix Presentation 4.0, or Xenapp 5, and are there any important differences in retrieving this information in either scenario? Currently my software is a client that connects to a service on a server, and the primary means of identification are computer name and IP Address. When installed on a Citrix Presentation server, all running instances currently show the same Computer Name and IP Address, which are those of the server. My application is written in VB 6.0, however I am looking to implement the new feature in C# .NET. Any help or clarification on the question itself would be appreciated, as I am not experienced with developing for Citrix thin clients.

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• SQL GROUP BY with "default values"

  - by Christoph Schiessl

  I'm trying to create SELECT statement with a GROUP BY clause, which should return "default values". Imagine the following simple MySQL table: CREATE TABLE `tracker` ( `id` INTEGER PRIMARY KEY auto_increment, `date` DATETIME NOT NULL, `customer_id` INTEGER NOT NULL ); The table contains only one record: INSERT INTO `tracker` (`date`, `customer_id`) VALUES('2010-05-03', 1); After wards I'm executing the following SQL query: SELECT DATE(`date`), COUNT(customer_id) FROM tracker WHERE DATE(`date`) >= '2010-05-01' AND DATE(`date`) <= '2010-05-05' GROUP BY DATE(`date`) ORDER BY DATE(`date`); And get the expected result set: +----+---------------------+-------------+ | id | date | customer_id | +----+---------------------+-------------+ | 1 | 2010-05-10 00:00:00 | 1 | +----+---------------------+-------------+ However, I would like the result set to look like this: +--------------+--------------------+ | DATE(`date`) | COUNT(customer_id) | +--------------+--------------------+ | 2010-05-01 | 0 | | 2010-05-02 | 0 | | 2010-05-03 | 1 | | 2010-05-04 | 0 | | 2010-05-05 | 0 | +--------------+--------------------+ Is it possible to achieve this behavior?

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• Data Access from single table in sql server 2005 is too slow

  - by Muhammad Kashif Nadeem

  Following is the script of table. Accessing data from this table is too slow. SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[Emails]( [id] [int] IDENTITY(1,1) NOT NULL, [datecreated] [datetime] NULL CONSTRAINT [DF_Emails_datecreated] DEFAULT (getdate()), [UID] [nvarchar](250) COLLATE Latin1_General_CI_AS NULL, [From] [nvarchar](100) COLLATE Latin1_General_CI_AS NULL, [To] [nvarchar](100) COLLATE Latin1_General_CI_AS NULL, [Subject] [nvarchar](max) COLLATE Latin1_General_CI_AS NULL, [Body] [nvarchar](max) COLLATE Latin1_General_CI_AS NULL, [HTML] [nvarchar](max) COLLATE Latin1_General_CI_AS NULL, [AttachmentCount] [int] NULL, [Dated] [datetime] NULL ) ON [PRIMARY] Following query takes 50 seconds to fetch data. select id, datecreated, UID, [From], [To], Subject, AttachmentCount, Dated from emails If I include Body and Html in select then time is event worse. indexes are on: id unique clustered From Non unique non clustered To Non unique non clustered Tabls has currently 180000+ records. There might be 100,000 records each month so this will become more slow as time will pass. Does splitting data into two table will solve the problem? What other indexes should be there?

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• Using sizeof operator on a typedef-ed struct

  - by sskanitk

  This might be something too obvious. However, I couldn't find the specific answer though many stackoverflow threads talk about different aspects of this. typedef struct _tmp { unsigned int a; unsigned int b; } tmp; int main() { int c=10; if (c <= sizeof tmp) { printf("less\n"); } else { printf("more\n"); } return 0; } I compile this prog as - g++ -lstdc++ a.cpp I get an error - expected primary-expression before ‘)’ token I think I am missing something very obvious and straightforward. But can't seem to pinpoint it :-/ Thanks!

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• Does php mvc framework agavi use CRUD compliant to REST?

  - by txwikinger

  The agavi framework uses the PUT request for create and POST for updating information. Usually in REST this is used the other way around (often referring to POST adding information while PUT replacing the whole data record). If I understand it correctly, the important issue is that PUT must be idempotent, while POST does not have this requirement. Therefore, I wounder how creating a new record can be idempotent (i.e. multiple request do not lead to multiple creations of a record) in particular when usually the ORM uses an id as a primary key and the id of a new record would not be known to the client (since it is autocreated in the database), hence cannot be part of the request. How does agavi maintain the requirement of idempotence in light of this for the PUT request. Thanks.

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• How do you access byte level information in JavaScript?

  - by JustSmith

  The generally accepted answer is that you can't. However there is mounting evidence that this is not true based on the existence of projects that read in types of data that are not basic HTML types. Some projects that do this are the JavaScript version of ProtoBuf and Smokescreen. Smokescreen is a flash interpreter written in JS so if it is not possible to get at the bytes directly how are these projects working around this? The source to Smokescreen can be found here. I have looked it over but with JS not being my primary language right now the solution eludes me.

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• TSQL ID generation

  - by Markus

  Hi. I have a question regarding locking in TSQL. Suppose I have a the following table: A(int id, varchar name), where id is the primary key, but is NOT an identity column. I want to use the following pseudocode to insert a value into this table: lock (A) uniqueID = GenerateUniqueID() insert into A values (uniqueID, somename) unlock(A) How can this be accomplished in terms of TSQL? The computation of the next id should be done with the table A locked in order to avoid other sessions to do the same operation at the same time and get the same id.

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• MySQL Query: Winning Auction Bid

  - by mabwi

  I have a small Bidding system that I'm using for a fantasy auction draft. I'm trying to use the below query to pull up the max bids on each player. However, it's not actually giving me the max bid, it's just giving me the first one entered in to the database. SELECT Bid.id FROM bids AS Bid WHERE Bid.active =1 GROUP BY player_id HAVING MAX( Bid.amount ) Here's the Bid table layout, in case it helps: CREATE TABLE IF NOT EXISTS `bids` ( `id` int(10) NOT NULL AUTO_INCREMENT, `user_id` int(10) NOT NULL, `player_id` int(10) NOT NULL, `amount` int(6) NOT NULL, `timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, `winning_bid` int(1) NOT NULL DEFAULT '0', `active` int(1) NOT NULL DEFAULT '1', PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 ;

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• Is there a way to rewrite the SQL query efficiently

  - by user320587

  hi, I have two tables with following definition TableA TableB ID1 ID2 ID3 Value1 Value ID1 Value1 C1 P1 S1 S1 C1 P1 S2 S2 C1 P1 S3 S3 C1 P1 S5 S4 S5 The values are just examples in the table. TableA has a clustered primary key ID1, ID2 & ID3 and TableB has p.k. ID1 I need to create a table that has the missing records in TableA based on TableB The select query I am trying to create should give the following output C1 P1 S4 To do this, I have the following SQL query SELECT DISTINCT TableA.ID1, TableA.ID2, TableB.ID1 FROM TableA a, TableB b WHERE TableB.ID1 NOT IN ( SELECT DISTINCT [ID3] FROM TableA aa WHERE a.ID1 == aa.ID1 AND a.ID2 == aa.ID2 ) Though this query works, it performs poorly and my final TableA may have upto 1M records. is there a way to rewrite this more efficiently. Thanks for any help, Javid

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• Why is autorelease especially dangerous/expensive for iPhone applications?

  - by e.James

  I'm looking for a primary source (or a really good explanation) to back up the claim that the use of autorelease is dangerous or overly expensive when writing software for the iPhone. Several developers make this claim, and I have even heard that Apple does not recommend it, but I have not been able to turn up any concrete sources to back it up. SO references: autorelease-iphone Why does this create a memory leak (iPhone)? Note: I can see, from a conceptual point of view, that autorelease is slightly more expensive than a simple call to release, but I don't think that small penalty is enough to make Apple recommend against it. What's the real story?

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• How to force restart a Windows box using VBScript?

  - by tloach

  I'm trying to find a way to force Windows to reboot, and I am running into issues. I've tried Set OpSysSet = GetObject("winmgmts:{authenticationlevel=Pkt," _ & "(Shutdown)}").ExecQuery("select * from Win32_OperatingSystem where "_ & "Primary=true") for each OpSys in OpSysSet retVal = OpSys.Reboot() next I've also tried using the shutdown -f -r command, and in both cases I sometimes get no response, and if I try again I get an error saying "Action could not complete because the system is shutting down" even though no matter how long I leave it it doesn't shut down, it still allows me to start new programs, and doing a shutdown -a gives the same error. How can a script be used to force Windows to reboot?

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• Perfect hash in Scala.

  - by Lukasz Lew

  I have some class C: class C (...) { ... } I want to use it to index an efficient map. The most efficient map is an Array. So I add a "global" "static" counter in companion object to give each object unique id: object C { var id_counter = 0 } In primary constructor of C, with each creation of C I want to remember global counter value and increase it. Question 1: How to do it? Now I can use id in C objects as perfect hash to index array. But array does not preserve type information like map would, that a given array is indexed by C's id. Question 2: Is it possible to have it with type safety?

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• InvalidOperationException sequence contains more than one element even when only one element

  - by user310256

  I have three tables, tblCompany table, tblParts table and a link table between them tblLinkCompanyParts. Since tblLinkCompanyParts is a link table so the columns that it has are LinkCompanyPartID(primary key), CompanyID from tblCompany table and PartID from tblParts as foreign keys. I have tied them up in the dbml file. In code if I write LinkCompanyParts.Parts (where LinkCompanyParts is an object of the tblLinkCompanyParts type) to get to the corresponding Part object I get the "InvalidOperationException: Sequence constains more than one element". I have looked at the data in the database and there is only one Parts record associated with the LinkCompanyPartID. The stack trace reads like at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source) at System.Data.Linq.EntityRef`1.get_Entity() at ... I read about SingleOrDefault vs FirstOrDefault but since the link table should have a one-one mapping therefore I think SingleOrDefault should work and besides "SingleOrDefault" statement is being generated behind the scenes in the designer.cs file at the following line return this._Part.Entity; Any ideas?

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• What is lisp used for today and where do you think it's going ?

  - by ldigas

  Never been a lisp user, so don't take me as too dense while reading this. But what is lisp used for today ? I know there are several variants of the language in existence, at least one which will keep it alive commercially for a while longer (AutoLisp, VisualLisp - pretty big support from Autodesk) ... but I don't meet everyday people using it. So if you can shed some light on the matter - what is it's primary target market nowadays ? And what do you believe its future will be ... will it become just another support language in few apps, or is it going somewhere ? Also, apart from "an editor whose name shall not be spoken" what other apps keep it as a support language ?

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• How to save array of integer numbers in a column in SQL Server 2005

  - by hamed

  I have a table in SQL Server 2005 with the following properties: Users (UserID, Username, Password) where UserID is primary key I want to save an array of integer numbers in the password attribute in the Users table. -------------------- 0 1 2 3 -------------------- 1543 6543 7658 8765 -------------------- I plan to save this into the password column. On the other hand I use pictures instead of texts for password and each picture has a code (4 digit) and a password include 4 picture that produce 16 digit. I want to save these 16 digits (array of Ints) into the Password column please help me. thanks

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• Efficiently generate a 16-character, alphanumeric string

  - by ensnare

  I'm looking for a very quick way to generate an alphanumeric unique id for a primary key in a table. Would something like this work? def genKey(): hash = hashlib.md5(RANDOM_NUMBER).digest().encode("base64") alnum_hash = re.sub(r'[^a-zA-Z0-9]', "", hash) return alnum_hash[:16] What would be a good way to generate random numbers? If I base it on microtime, I have to account for the possibility of several calls of genKey() at the same time from different instances. Or is there a better way to do all this? Thanks.

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• Google App Engine update an object from servlet not working ?

  - by Frank

  I use the following code to update an object from servlet in Google App Engine : String Time_Stamp=Get_Date_Format(6),query="select from "+Contact_Info_Entry.class.getName()+" where Contact_Id == '"+Contact_Id+"' order by Contact_Id desc"; PersistenceManager pm=null; try { pm=PMF.get().getPersistenceManager(); // note that this returns a list, there could be multiple, DataStore does not ensure uniqueness for non-primary key fields List<Contact_Info_Entry> results=(List<Contact_Info_Entry>)pm.newQuery(query).execute(); Contact_Info_Entry A_Contact_Entry=results.get(0); A_Contact_Entry.Extra_10=Time_Stamp; pm.makePersistent(A_Contact_Entry); } catch (Exception e) { Send_Email(Email_From,Email_To,"Check_License_Servlet Error [ "+Time_Stamp+" ]",new Text(e.toString()+"\n"+Get_Stack_Trace(e)),null); } finally { pm.close(); } The value "[ 2010-05-13 Thu 15:58:31 ]" was in A_Contact_Entry.Extra_10, but it seems "pm.makePersistent(A_Contact_Entry);" was not executed. The object was not updated and there was no error message, why ? How to fix it ?

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• Django User "per project" group assignation

  - by Ben G

  Hi, Here's my problem : my site has users, which can create projects, and access other user's projects. Each project can assign different rights to users. So, i could have Project A : user "John" is in group "manager" , and Project "B" user "John" is in group "worker". How could I use the Django User authentication model to do that ? From a SQL point a view, what i would like is to be able to add "project_id" in the primary key for the "auth_user_groups" table. I don't think profile is of any help here. Any advice ? UPDATE : "worker" and "manager" are just two examples of the permission group (or "roles") that my application defines. There will be more in the future. Eg : i will probably also have "admin", "reporting", etc...

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• Aldon and .Net Development

  - by David Stratton

  I'm looking for feedback from .Net developers who have experience with Aldon as a lifecycle management platform. We're seriously considering using Aldon for lifecycle management including source control, automated builds, etc. I know there are a lot of other options out there, but ours is primary an AS/400 shop (with AS/400 programmers outnumbering .Net developers 6 to 1), and Aldon is used already by our iSeries team. The benefit we're looking for is having one lifecycle management suite. Basically, I'm looking for opinions from people who have used Aldon and another set of tools (perhaps TFS, or a combination of SVN, Cruise Control, etc). If you've worked with both, do you have a recommendation on whether this is a good idea, or a bad idea? It's obviously a big choice, so any feedback would be helpful.

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• Oracle - correlated subquery problems

  - by FrustratedWithFormsDesigner

  I have this query: select acc_num from (select distinct ac_outer.acc_num, ac_outer.owner from ac_tab ac_outer where (ac_outer.owner = '1234567') and ac_outer.owner = (select sq.owner from (select a1.owner from ac_tab a1 where a1.acc_num = ac_outer.acc_num order by a1.a_date desc, a1.b_date desc, a1.c_date desc) sq where rownum = 1) order by dbms_random.value()) subq order by acc_num; The idea is to get all acc_nums (not a primary key) from ac_tab, that have an owner of 1234567. Since an acc_num in ac_tab could have changed owners over time, I am trying to use the inner correlated subqueries to ensure that an acc_num is returned ONLY if it's most recent owner is 12345678. Naturally, it doesn't work (or I wouldn't be posting here ;) ) Oracle gives me an error: ORA-000904 ac_outer.acc_num is an invalid identifier. I thought that ac_outer should be visible to the correlated subqueries, but for some reason it's not. Is there a way to fix the query, or do I have to resort to PL/SQL to solve this? (Oracle verison is 10g)

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• Linux application that bundles multiple incoming audio and video streams into one container file?

  - by StackedCrooked

  I've been assigned to implement a video on-demand service for a local university. Different aspects of the lectures (video, audio, screen cast, white board) will be recorded. During a lecture all these data streams arrive at one Linux server. This server should transcode and bundle all these streams into one container (Matroska) file. My options seem to be: Write a GStreamer application do something with FFMPEG do something with VLC ...? Has anyone done something similar in the past? Can you recommend something? Edit For those interested, here are a few of my findings: Matroska is not a good format for streaming (it's possible, but it's not its primary intent) For Flash streaming you can use MPEG4 If you want to combine different videos into one video where each subvideo occupies a rectangular portion of the total screen, then this GStreamer script is useful (I found it on this blog post). Desktop capture works fine with VLC

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• MySQL get row closest to NOW()

  - by Christopher McCann

  I have a table with User data such as name, address etc and another table which has a paragraph of text about the user. The reason that they are separate is because we need to record all the old about data. So if the user changes their paragraph - the old one should still be stored. Each bit of about data has a primary key aboutMeID. What I want to do is have a join that pulls their name, address etc and the latest bit of aboutMe data from the other table. I am not sure though how I can order the join to only get the latest about me data. Can someone help?

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