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  • Does the optimizer filter subqueries with outer where clauses

    - by Mongus Pong
    Take the following query: select * from ( select a, b from c UNION select a, b from d ) where a = 'mung' Will the optimizer generally work out that I am filtering a on the value 'mung' and consequently filter mung on each of the queries in the subquery. OR will it run each query within the subquery union and return the results to the outer query for filtering (as the query would perhaps suggest) In which case the following query would perform better : select * from ( select a, b from c where a = 'mung' UNION select a, b from d where a = 'mung' ) Obviously query 1 is best for maintenance, but is it sacrificing much performace for this? Which is best?

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  • C# using the "this" keyword in this situation?

    - by Alex
    Hi, I've completed a OOP course assignment where I design and code a Complex Number class. For extra credit, I can do the following: Add two complex numbers. The function will take one complex number object as a parameter and return a complex number object. When adding two complex numbers, the real part of the calling object is added to the real part of the complex number object passed as a parameter, and the imaginary part of the calling object is added to the imaginary part of the complex number object passed as a parameter. Subtract two complex numbers. The function will take one complex number object as a parameter and return a complex number object. When subtracting two complex numbers, the real part of the complex number object passed as a parameter is subtracted from the real part of the calling object, and the imaginary part of the complex number object passed as a parameter is subtracted from the imaginary part of the calling object. I have coded this up, and I used the this keyword to denote the current instance of the class, the code for my add method is below, and my subtract method looks similar: public ComplexNumber Add(ComplexNumber c) { double realPartAdder = c.GetRealPart(); double complexPartAdder = c.GetComplexPart(); double realPartCaller = this.GetRealPart(); double complexPartCaller = this.GetComplexPart(); double finalRealPart = realPartCaller + realPartAdder; double finalComplexPart = complexPartCaller + complexPartAdder; ComplexNumber summedComplex = new ComplexNumber(finalRealPart, finalComplexPart); return summedComplex; } My question is: Did I do this correctly and with good style? (using the this keyword)?

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  • implement bank using python programming

    - by prajakta
    Write software for a bank. The program should be menu driven with the facility for bank employees to perform various operations. It should be written using all concepts of Object Oriented programming. You should be able to save your data in a file and read it back (because the bank people will shut down their computers when they go home :p ) Guidelines: The program may select to implement classes like Bank, Account, Savings Account, Fixed Deposit account, Customer, Depositor, Borrower, Transaction, etc.

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  • What is the Proper approach for Constructing a PhysicalAddress object from Byte Array

    - by Paul Farry
    I'm trying to understand what the correct approach for a constructor that accepts a Byte Array with regard to how it stores it's data (specifically with PhysicalAddress) I have an array of 6 bytes (theAddress) that is constructed once. I have a source array of 18bytes (theAddresses) that is loaded from a TCP Connection. I then copy the 6bytes from theAddress+offset into theAddress and construct the PhysicalAddress from it. Problem is that the PhysicalAddress just stores the Reference to the array that was passed in. Therefore if you subsequently check the addresses they only ever point to the last address that was copied in. When I took a look inside the PhysicalAddress with reflector it's easy to see what's going on. public PhysicalAddress(byte[] address) { this.changed = true; this.address = address; } Now I know this can be solved by creating theAddress array on each pass, but I wanted to find out what really is the best practice for this. Should the constructor of an object that accepts a byte array create it's own private Variable for holding the data and copy it from the original Should it just hold the reference to what was passed in. Should I just created theAddress on each pass in the loop

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  • Should java try blocks be scoped as tightly as possible?

    - by isme
    I've been told that there is some overhead in using the Java try-catch mechanism. So, while it is necessary to put methods that throw checked exception within a try block to handle the possible exception, it is good practice performance-wise to limit the size of the try block to contain only those operations that could throw exceptions. I'm not so sure that this is a sensible conclusion. Consider the two implementations below of a function that processes a specified text file. Even if it is true that the first one incurs some unnecessary overhead, I find it much easier to follow. It is less clear where exactly the exceptions come from just from looking at statements, but the comments clearly show which statements are responsible. The second one is much longer and complicated than the first. In particular, the nice line-reading idiom of the first has to be mangled to fit the readLine call into a try block. What is the best practice for handling exceptions in a funcion where multiple exceptions could be thrown in its definition? This one contains all the processing code within the try block: void processFile(File f) { try { // construction of FileReader can throw FileNotFoundException BufferedReader in = new BufferedReader(new FileReader(f)); // call of readLine can throw IOException String line; while ((line = in.readLine()) != null) { process(line); } } catch (FileNotFoundException ex) { handle(ex); } catch (IOException ex) { handle(ex); } } This one contains only the methods that throw exceptions within try blocks: void processFile(File f) { FileReader reader; try { reader = new FileReader(f); } catch (FileNotFoundException ex) { handle(ex); return; } BufferedReader in = new BufferedReader(reader); String line; while (true) { try { line = in.readLine(); } catch (IOException ex) { handle(ex); break; } if (line == null) { break; } process(line); } }

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  • Passing arguments and values form HTML to jQuery (events)

    - by Jaroslav Moravec
    What is the practice to pass arguments from HTML to jQuery events function. For example getting id of row from db: <tr class="jq_killMe" id="thisItemId-id"> ... </tr> and jQuery: $(".jq_killMe").click(function () { var tmp = $(this).attr('id).split("-"); var id = tmp[0] // ... } What's the best practise, if I want to pass more than one argument? Is it better not to use jQuery? For example: <tr onclick="killMe('id')"> ... </tr> I didn't find the answer on my question, I will be glad even for links. Thanks.

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  • What ways are there for cleaning an R environment from objects?

    - by Tal Galili
    I know I can use ls() and rm() to see and remove objects that exist in my environment. However, when dealing with "old" .RData file, one needs to sometimes pick an environment a part to find what to keep and what to leave out. What I would like to do, is to have a GUI like interface to allow me to see the objects, sort them (for example, by there size), and remove the ones I don't need (for example, by a check-box interface). Since I imagine such a system is not currently implemented in R, what ways do exist? What do you use for cleaning old .RData files? Thanks, Tal

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  • Where to store selected language on multilingual site: session/cookies or url?

    - by tig
    I have a site that has all its content translated to multiple languages and has no accounts (to set prefered language there). I can detect preferred language using Accept-Language, ip or anything else. I have 3 ways to store user language selection: Detect language and store it in cookie/session and allow switching language (and also store it in cookie/session) Use detected language if there is no language specified in url, and show links to url with different language Use default site language and show links to other languages Storing langage in url can be of any type: different domain, subdomain, or somewhere in url I think about first case as it allows me to send one url to anyone and it will be presented to them in their preferred language. But another opinion is that different language means different data, so it must have different link.

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  • Choosing between instance methods and separate functions?

    - by StackedCrooked
    Adding functionality to a class can be done by adding a method or by defining a function that takes an object as its first parameter. Most programmers that I know would choose for the solution of adding a instance method. However, I sometimes prefer to create a separate function. For example, in the example code below Area and Diagonal are defined as separate functions instead of methods. I find it better this way because I think these functions provide enhancements rather than core functionality. Is this considered a good/bad practice? If the answer is "it depends", then what are the rules for deciding between adding method or defining a separate function? class Rect { public: Rect(int x, int y, int w, int h) : mX(x), mY(y), mWidth(w), mHeight(h) { } int x() const { return mX; } int y() const { return mY; } int width() const { return mWidth; } int height() const { return mHeight; } private: int mX, mY, mWidth, mHeight; }; int Area(const Rect & inRect) { return inRect.width() * inRect.height(); } float Diagonal(const Rect & inRect) { return std::sqrt(std::pow(static_cast<float>(inRect.width()), 2) + std::pow(static_cast<float>(inRect.height()), 2)); }

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  • What are some good ways to write PHP application with modules support?

    - by Gabriel
    Hi, I'm starting to write a application in php with one of my friends and was wondering, if you have any advice on how to implement module support into our application. Or is there a way how to automatically load modules written in php by a php application? Or should i just rely on __autoload function? And we are not using any kind of framework, for now at least.

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  • Rank Source Control Options-VSS vs CVS vs none vs your own hell

    - by Roman A. Taycher
    It seems like a lot of people here and on many programmer wikis/blogs/ect. elsewhere really dislike VSS. A lot of people also have a serious dislike for cvs. In many places I have heard a lot of differing opinions on whether or not using VSS or cvs is better or worse then using no source control, please rate the worst and explain why!!!!! you rated them this way. Feel free to throw in your own horrible system in the rankings. If you feel it depends on the circumstances try to explain the some of the different scenarios which lead to different rankings. (note:I see a lot of discussion of what is better but little of what is worse.) second note: while both answers are nice I'm looking less for good replacements and more for a comparison of which is worse and more importantly why!

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  • Reverse search in Hibernate Search

    - by Javi
    Hello, I'm using Hibernate Search (which uses Lucene) for searching some Data I have indexed in a directory. It works fine but I need to do a reverse search. By reverse search I mean that I have a list of queries stored in my database I need to check which one of these queries match with a Data object each time Data Object is created. I need it to alert the user when a Data Object matches with a Query he has created. So I need to index this single Data Object which has just been created and see which queries of my list has this object as a result. I've seen Lucene MemoryIndex Class to create an index in memory so I can do something like this example for every query in a list (though iterating in a Java list of queries would not be very efficient): //Iterating over my list<Query> MemoryIndex index = new MemoryIndex(); //Add all fields index.addField("myField", "myFieldData", analyzer); ... QueryParser parser = new QueryParser("myField", analyzer); float score = index.search(query); if (score > 0.0f) { System.out.println("it's a match"); } else { System.out.println("no match found"); } The problem here is that this Data Class has several Hibernate Search Annotations @Field,@IndexedEmbedded,... which indicated how fields should be indexed, so when I invoke index() method on the FullTextEntityManager instance it uses this information to index the object in the directory. Is there a similar way to index it in memory using this information? Is there a more efficient way of doing this reverse search? Thanks

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  • What are great _specific_ usability guidelines?

    - by Jilles
    Usability is extremely important, and yet there are so many products that violate a lot of rules. There are several questions on StackOverflow that are about usability (see: link1, link2, link3), however what I feel is missing still is a comprehensive list of usability "tactics": concrete examples of what (not) to do for a web application. Please don't add references to books. Please list one example per answer so that we can use the voting to actually prioritize the list.

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  • Is there a standard practice for storing default application data?

    - by Rox Wen
    Our application includes a default set of data. The default data includes coefficients and other factors that are unlikely to ever change but still need to be update-able by the user. Currently, the original default data is stored as a populated class within the application. Data updates are stored to an external XML file. This design allows us to include a "reset" feature to restore the original default data. Our rationale for not storing defaults externally [e.g. XML file] was to minimize the risk of being altered. The overall volume of data doesn't warrant a database. Is there a standard practice for storing "default" application data?

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  • Which programming language to use for serious project?

    - by alex
    Hi! Which programming language to use for serious web project (price catalogue)? After some time of studying web PHP frameworks i got that: Codeigniter: good, but when i read about authorization (that 20% users can login correctly without party solutions), i am disappointed. Zend Framework: more serious, but raises questions about speed and i found only few examples. PHP: long time to understand PHP frameworks functionality

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  • What are the virtues of using XML comments in .NET?

    - by Michal Czardybon
    I can't understand the virtues of using XML comments. I know they can be converted into nice documentation external to the code, but the same can be achieved with the much more concise DOxygen syntax. In my opinion the XML comments are wrong, because: They obfuscate the comments and the code in general. (They are more difficult to read by humans). Less code can be viewed on a single screen, because "summary" and "/summary" take additional lines. They suggest that all method parameters have to be commented, whereas 90% of them are obvious and SHOULD be left not commented. The only problem I have with this is that my point of view seems to be in minority. Why?

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  • Overcoming C limitations for large projects

    - by Francisco Garcia
    One aspect where C shows its age is the encapsulation of code. Many modern languages has classes, namespaces, packages... a much more convenient to organize code than just a simple "include". Since C is still the main language for many huge projects. How do you to overcome its limitations? I suppose that one main factor should be lots of discipline. I would like to know what you do to handle large quantity of C code, which authors or books you can recommend.

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  • What is the best way to store site configuration data?

    - by DaveDev
    I have a question about storing site configuration data. We have a platform for web applications. The idea is that different clients can have their data hosted and displayed on their own site which sits on top of this platform. Each site has a configuration which determines which panels relevant to the client appear on which pages. The system was originally designed to keep all the configuration data for each site in a database. When the site is loaded all the configuration data is loaded into a SiteConfiguration object, and the clients panels are generated based on the content of this object. This works, but I find it very difficult to work with to apply change requests or add new sites because there is so much data to sift through and it's difficult maintain a mental model of the site and its configuration. Recently I've been tasked with developing a subset of some of the sites to be generated as PDF documents for printing. I decided to take a different approach to how I would define the configuration in that instead of storing configuration data in the database, I wrote XML files to contain the data. I find it much easier to work with because instead of reading meaningless rows of data which are related to other meaningless rows of data, I have meaningful documents with semantic, readable information with the relationships defined by visually understandable element nesting. So now with these 2 approaches to storing site configuration data, I'd like to get the opinions of people more experienced in dealing with this issue on dealing with these two approaches. What is the best way of storing site configuration data? Is there a better way than the two ways I outlined here? note: StackOverflow is telling me the question appears to be subjective and is likely to be closed. I'm not trying to be subjective. I'd like to know how best to approach this issue next time and if people with industry experience on this could provide some input.

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  • [MySQL/PHP] Avoid using RAND()

    - by Andrew Ellis
    So... I have never had a need to do a random SELECT on a MySQL DB until this project I'm working on. After researching it seems the general populous says that using RAND() is a bad idea. I found an article that explains how to do another type of random select. Basically, if I want to select 5 random elements, I should do the following (I'm using the Kohana framework here)? If not, what is a better solution? Thanks, Andrew <?php final class Offers extends Model { /** * Loads a random set of offers. * * @param integer $limit * @return array */ public function random_offers($limit = 5) { // Find the highest offer_id $sql = ' SELECT MAX(offer_id) AS max_offer_id FROM offers '; $max_offer_id = DB::query(Database::SELECT, $sql) ->execute($this->_db) ->get('max_offer_id'); // Check to make sure we're not trying to load more offers // than there really is... if ($max_offer_id < $limit) { $limit = $max_offer_id; } $used = array(); $ids = ''; for ($i = 0; $i < $limit; ) { $rand = mt_rand(1, $max_offer_id); if (!isset($used[$rand])) { // Flag the ID as used $used[$rand] = TRUE; // Set the ID if ($i > 0) $ids .= ','; $ids .= $rand; ++$i; } } $sql = ' SELECT offer_id, offer_name FROM offers WHERE offer_id IN(:ids) '; $offers = DB::query(Database::SELECT, $sql) ->param(':ids', $ids) ->as_object(); ->execute($this->_db); return $offers; } }

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