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• PostgreSQL: Why does this simple query not use the index?

  - by David

  I have a table t with a column c, which is an int and has a btree index on it. Why does the following query not utilize this index? explain select c from t group by c; The result I get is: HashAggregate (cost=1005817.55..1005817.71 rows=16 width=4) -> Seq Scan on t (cost=0.00..946059.84 rows=23903084 width=4) My understanding of indexes is limited, but I thought such queries were the purpose of indexes.

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• Does Win 2008 r2 x64 server come with .net 3 sp1 package already installed?

  - by luckyluke

  same as in title? I have a test server with mentioned OS and my app is .net 3.5 based. I do want to know if win 2008 r2 comes with service pack 1 for .net 3.5 from the box. And does it come with .net 3.5 sp1 family update as WELL, since after I downloaded the update, the installer says I do not have software required to update. Could some win 2008 guru perhaps explain it to me? thanks luke

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• Regex expression in plain english

  - by Sebi

  I'm working on a new Java project and therefore im reading the already existing code. On a very important part of the code if found the following regex expression and i can't really tell what they are doing. Anybody can explain in plain english what they do?? 1) [^,]*|.+(,).+ 2) (\()?\d+(?(1)\))

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• JSF data transfer between UI and business layer

  - by Ram

  Hi, We are using JSF in UI, Spring in business layer, Hibernate in persistence layer. Now my question is how to pass data from the JSF UI to spring business layer. Can I directly use my business object in my backing bean or should I transfer data between the layer through DTO? Can one explain me with clear explanation if possible with piece of code and that related websites?

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• MySQL won't use index for query?

  - by Jack Sleight

  I have this table: CREATE TABLE `point` ( `id` INT(11) NOT NULL AUTO_INCREMENT, `siteid` INT(11) NOT NULL, `lft` INT(11) DEFAULT NULL, `rgt` INT(11) DEFAULT NULL, `level` SMALLINT(6) DEFAULT NULL, PRIMARY KEY (`id`), KEY `point_siteid_site_id` (`siteid`), CONSTRAINT `point_siteid_site_id` FOREIGN KEY (`siteid`) REFERENCES `site` (`id`) ON DELETE CASCADE ) ENGINE=INNODB AUTO_INCREMENT=35 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci And this query: SELECT * FROM `point` WHERE siteid = 1; Which results in this EXPLAIN information: +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ | 1 | SIMPLE | point | ALL | point_siteid_site_id | NULL | NULL | NULL | 6 | Using where | +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ Question is, why isn't the query using the point_siteid_site_id index?

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• Character Sets explained for Dummies!

  - by Imran

  I don't think i fully understand character sets so i was wondering if anyone would be kind enough to explain it in layman's terms with examples ( for Dummies).I know there is utf8, latin1, ascii ect The more answers the better really. Thank you in advance;-)

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• How can i resolve the N+1 Selects problem ?

  - by Maxime ARNSTAMM

  Hello everyone, I have trouble understanding how to avoid the n+1 select in jpa or hibernate. From what i read, there's the 'left join fetch', but i'm not sure if it still works with more than one list (oneToMany).. Could someone explain it to me, or give me a link with a clear complete explanation please ? I'm sorry if this is a noob question, but i can't find a real clear article or doc on this issue. Thanks

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• IoC and DI framework for .Net applications

  - by Lijo

  Hi Can you please explain how the following three are different in their intent? 1) Policy Injection Application Block 2) Structure Map IoC Managed 3) Managed Extensibility Framework In terms of the common tasks they do, which is simpler/aligned with generics and C# 3.0 ? Thanks Lijo

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• How to resolve “Unit JclCompression was compiled with a different version of sevenzip.IOutArchive”?

  - by John

  Hello, There is already a similar question(link).The thing is I don't understand what unit I have to delete. I have installed the latest JCL library and added 'JclCompression' to the uses list in a unit and I get the error: "Unit JclCompression was compiled with a different version of sevenzip.IOutArchive". Please explain to me in a simpler way how to resolve the problem. Thanks in advance!

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• A view model mvvm design issue

  - by Chen Kinnrot

  the best way to explain is with example so: this is the model public class Person { public int age; public string name; } this is the view model public class PersonVM { } my question is: should the vm expose the person to the datga template or encapsulate the model properties with his own properties?

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• Control separate Menu Component

  - by dmschenk

  I'm trying to create a menu component for my flashbuilder app but when I separate the menu from the main application it stops working. Can someone show an example of how to do this? Also if this is a bad idea could some explain why? Thanks Dave

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• Why does Javascript's OR return a value other than true/false?

  - by Fletcher Moore

  I saw this construction in order to get the browser viewport width: function () { return window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth; } I understand the browser quirks involved. What I don't understand is why || returns the value. So I tried this alert(undefined || 0 || 3); and sure enough, it alerts 3. I find this bizarre, because I expect true or false. Could anyone explain what's going on?

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• php: session_start() error

  - by Syom

  I have a file, which starts <?php session_start();?>, and it returns an error Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\xampp2\htdocs\index.php:1) in C:\xampp2\htdocs\index.php on line 3 and now take a look at the moment, i can't anderstand anyway when i copy the all content of my file into another file, it start working. can somebody explain how can it happen. thanks update i havent't any white spaces, at least i can't see them

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• Why is git better than Subversion?

  - by Ben Mills

  I've been using Subversion for a few years and after using SourceSafe, I just love Subversion. Combined with TortoiseSVN, I can't really imagine how it could be any better. Yet there's a growing number of developers claiming that Subversion has problems and that we should be moving to the new breed of distributed version control systems, such as Git. Can anyone explain how Git improves upon Subversion?

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• Languages for implementing decision trees

  - by Shailesh Tainwala

  What would be a good choice of programming language in which to implement a decision tree? The results of the implementation will be for personal use only, so no need to consider ability to publish etc. I have heard that Octave is a good option, can anyone explain why a matrix based language is recommended for implementing decision trees?

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• What is the meaning of ": base" in the costructor definition ?

  - by DotNetBeginner

  What is the meaning of ": base" in the costructor of following class(MyClass) ? Please explain the concept behind constructor definition given below for class MyClass. public class MyClass: WorkerThread { public MyClass(object data): base(data) { // some code } } public abstract class WorkerThread { private object ThreadData; private Thread thisThread; public WorkerThread(object data) { this.ThreadData = data; } public WorkerThread() { ThreadData = null; } }

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• QWebFrame::evaluateJavaScript vs. script-tag in HTML

  - by jwg

  Hi, I want to develop an application that uses QtWebKit and JQuery. What I need to know is, is there any difference between reading JQuery from a file and evaluateJavaScript it, or embedding it as a script tag within the "page" that is displayed within the widget? If there is a difference, I am curious if anyone could explain why it would be. As far as I understood it, evaluateJavaScript() would feed the script parameter to the JavaScript interpreter, which interprets it in the current page's context. Thanks.

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• Can you return an array from a JAX-WS @WebMethod?

  - by LES2

  I'm pretty sure you can, but in addition to answering the question in the title, could you also explain the pros, cons, caveats, if any, to doing so? I know that you can't return a List, Set, Collection, Map, or any interface, from a WebMethod (which is stupid, IMO, but I don't know what the design reasons were should I should probably withhold judgment). Thanks for any advice. -- LES

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• zip -j command, what does the -j option mean?

  - by Simon Guo

  Wondering what is the -j option mean in the zip command. I found the explanation as following: -j Store just the name of a saved file (junk the path), and do not store directory names. By default, zip will store the full path (relative to the current path). But not quite sure what it is exact mean? Can anyone explain it using the following command as an example? C:\programs\zip -j myzipfile file1 file2 file3 Thank you.

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• Whats the significance of creating three db's in ruby and rails.

  - by piemesons

  Hello friends i am moving from php to ruby on rails. Suppose u want to create a application in ruby on rails rails depot -d mysql This will create a application depot with database mysql right..!!! Now config/database.yml has a definition of three databases ie depot_development, depot_test and depot_production under environment development , test and production respectiviely Whats the significance of creating these three databases.. (Please explain considering this is my first day with ruby on rails and i am takin help from Agile Web Development with Rails)

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• Whats the difference between new Foo; and new Foo();

  - by uberjumper

  Can someone please explain what is the different between calling new like: foo = new QtWidget(); I noticed alot of Qt's examples do this: foo = new QtWidget; I tried to Google this but didn't come up with anything.

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• Visual Studio appears to randomly adopt american keyboard layout

  - by HollyStyles

  Gah! this is really causing me hassle today. Suddenly without warning '@' (at symbol) and '"' (double quote) are trading places on my keyboard but ONLY in Visual Studio 2008 !!! I can't seem to find anything in help or online to explain/remedy this. Is there some keyboard shortcut I am inadvertantly executing?? I rebooted my PC and it went away for an hour or two and then suddenly came back. Oh the insanity :(

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• Basic tutorial for multithreading

  - by Russel

  Hi, I'm a coding newbie, but I really wanna learn how to do multithreading and event handling. Does anyone know of any good tutorials out there, or can they explain it to me in a nutshell?

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• Can somebody suggest good source for IMS?

  - by Raja Reddy

  I would like to learn working with IMS, can somebody suggest me a good source? I'm not sure if it matters to say that I have quite good exposure and experience with INSYNC DB2 and QMF. So anything that can depict and explain the advantages and disadvantages over IMS would be really helpful. Thanks for your help beforehand..

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• Running Rails as an embedded app inside of a gem

  - by randombits

  I'm trying to understand what exactly the above (in my question's Title) means? This is taken directly from the SpreeCommerce.com project: If you’re an experienced Rails developer you may be wondering where your app directory is. Spree actually runs as an embedded Rails app inside of your gem. How do you customize things then? We’ll cover that later in extensions. Source: http://spreecommerce.com/documentation/getting_started.html Can someone further explain what exactly it means when a Rails app is run "inside of your gem"

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