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• Are conditional subqueries optimized out, if the condition is false?

  - by Tobias Schulte

  I have a table foo and a table bar, where each foo might have a bar (and a bar might belong to multiple foos). Now I need to select all foos with a bar. My sql looks like this SELECT * FROM foo f WHERE [...] AND ($param IS NULL OR (SELECT ((COUNT(*))>0) FROM bar b WHERE f.bar = b.id)) with $param being replaced at runtime. The question is: Will the subquery be executed even if param is null, or will the dbms optimize the subquery out? We are using mysql, mssql and oracle. Is there a difference between these regarding the above?

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• How many double numbers are there between 0.0 and 1.0?

  - by polygenelubricants

  This is something that's been on my mind for years, but I never took the time to ask before. Many (pseudo) random number generators generate a random number between 0.0 and 1.0. Mathematically there are infinite numbers in this range, but double is a floating point number, and therefore has a finite precision. So the questions are: Just how many double numbers are there between 0.0 and 1.0? Are there just as many numbers between 1 and 2? Between 100 and 101? Between 10^100 and 10^100+1? Note: if it makes a difference, I'm interested in Java's definition of double in particular.

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• Executing ffmpeg from php running in apache

  - by foobar

  I was executing ffmpeg from php running inside apache. I used to get the error " error while loading shared libraries: libavdevice.so.52: cannot open shared object file: No such file or directory". It used to work perfectly if the php script was executed from the command prompt or ffpmeg was directly invoked from the command prompt. I followed the below steps to fix the apache error: Step 1: Check if the file “libavdevice.so.52? exists in the server using the following command. find / -name ‘libavdevice.so.*’ Step 2: You will get the directory in which the file “libavdevice.so.52? exists from the above command. Suppose the directory is “/usr/local/lib/” in this example. Step 3: You have to add the directory name in the file “/etc/ld.so.conf”. Step 4: Execute the command “ldconfig”. How did doing the above make a difference to apache?

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• Class.Class vs Namespace.Class for top level general use class libraries?

  - by Joan Venge

  Which one is more acceptable (best-practice)?: namespace NP public static class IO public static class Xml ... // extension methods using NP; IO.GetAvailableResources (); vs public static class NP public static class IO public static class Xml ... // extension methods NP.IO.GetAvailableResources (); Also for #2, the code size is managed by having partial classes so each nested class can be in a separate file, same for extension methods (except that there is no nested class for them) I prefer #2, for a couple of reasons like being able to use type names that are already commonly used, like IO, that I don't want to replace or collide. Which one do you prefer? Any pros and cons for each? What's the best practice for this case? EDIT: Also would there be a performance difference between the two?

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• Can VBScript determine the most recently modified (or added) file in a particular folder?

  - by Jimminy

  Hello, I have a script (or more accurately WILL have a script) that checks a folder and copies a file from this folder to a different location (will run once per day). The fileName that I'd like to copy from, however, changes based on the date. Basically, instead of setting the "strFilePath" to "C:\somePath\somePath2\myFile.txt" I would like to simply take the most recently modified (or added - does this make a difference in terms of the script??) in the "somePath2" folder and copy it to the destination. Bonus (but not completely necessary) would be to check in the script if the file was modified/added in the last 24 hours and only copy it over in that case. Thanks for your help!

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• C++ iterators & loop optimization

  - by Quantum7

  I see a lot of c++ code that looks like this: for( const_iterator it = list.begin(), const_iterator ite = list.end(); it != ite; ++it) As opposed to the more concise version: for( const_iterator it = list.begin(); it != list.end(); ++it) Will there be any difference in speed between these two conventions? Naively the first will be slightly faster since list.end() is only called once. But since the iterator is const, it seems like the compiler will pull this test out of the loop, generating equivalent assembly for both.

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• UIViewController: setToolbarItems vs navigationItem

  - by Paul Sanwald

  my application has a UIViewController subclass which is being managed by a UINavigationController. In the viewDidLoad of my UIViewController subclass, I was attempting to add a UIBarButtonItem to the toolbar like this: settingsButton = [[UIBarButtonItem alloc] initWithTitle:@"Settings" style:UIBarButtonItemStylePlain target:self action:@selector(viewSettings:)]; [self setToolbarItems:[NSArray arrayWithObject:settingsButton]]; this wasn't working out for me, so after some googling around, I tried this: [[self navigationItem] setRightBarButtonItem:settingsButton]; which worked out fine. from reading the UIViewController documentation, I'm still confused about why setToolbarItems wasn't working. I verified in the debugger that the button was in the toolbarItems array in the viewDidAppear method. the button itself just wasn't appearing on my toolbar. so, my question is, why didn't setToolbarItems work for me in the first code snippet? I don't have the toolbar configured in my xib for this view controller at all, if that makes a difference.

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• List filtering: list comprehension vs. lambda + filter

  - by Agos

  I happened to find myself having a basic filtering need: I have a list and I have to filter it by an attribute of the items. My code looked like this: list = [i for i in list if i.attribute == value] But then i thought, wouldn't it be better to write it like this? filter(lambda x: x.attribute == value, list) It's more readable, and if needed for performance the lambda could be taken out to gain something. Question is: are there any caveats in using the second way? Any performance difference? Am I missing the Pythonic Way™ entirely and should do it in yet another way (such as using itemgetter instead of the lambda)? Thanks in advance

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• javascript: what are immediate functions used for [duplicate]

  - by tkoomzaaskz

  This question already has an answer here: Why using self executing function in JavaScript? [duplicate] 4 answers I've been programming in JS since some time, but I have never came upon a need of using immediate functions, for example: (function(){ console.log('hello, I am an immediate function'); }()) What would be the difference if I just wrote: console.log('hello, I am an immediate function'); ? I don't have any access to this function anyway (it is not assigned anywhere). I think (but I'm not sure) that I can implement everything without immediate functions - so why do people use it?

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• How do I do division on HH:MM:SS format time strings in C#?

  - by Jake

  I have a series of times that are coming to me as strings from a web service. The times are formated as HH:MM:SS:000 (3 milisecond digits). I need to compare two times to determine if one is more than twice as long as the other: if ( timeA / timeB > 2 ) What's the simplest way to work with the time strings? If I was writing in Python this would be the answer to my question: Difference between two time intervals in Python Edit: What I'm really looking for is a way to get the ratio of timeA to timeB, which requires division, not subtraction. Unfortunately, the DateTime structure doesn't appear to have a division operator. Updated the question title to reflect this.

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• C++ deleting a pointer

  - by eSKay

  On this page, its written that One reason is that the operand of delete need not be an lvalue. Consider: delete p+1; delete f(x); Here, the implementation of delete does not have a pointer to which it can assign zero. Adding a number to a pointer shifts it forward in memory by those many number of sizeof(*p) units. So, what is the difference between delete p and delete p+1, and why would making the pointer 0 only be a problem with delete p+1?

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• Mac OS X 10.5 App "not supported on this architecture" cured by copying?

  - by JWWalker

  I have an app that updates itself over the internet, and the updated copy won't run on PowerPC machines (G5) running Leopard (10.5.8). Double-clicking the app produces a message saying "You can't open the application "appname" because it is not supported on this architecture." But here's the weird part: if I duplicate the app using the Finder or using a cp -R command, then the duplicate runs fine! And yet, if I do ls -laeR on both apps, the results are identical. I restarted the machine, and the difference between the two copies was still there. Sometimes, renaming the app made it run. After a few tries, I managed to rename it back to the original name and still have it run. If this was just on one machine, I'd dismiss it as disk corruption, cosmic rays, or a voodoo hex, but it was reported by a customer and then I reproduced it on my own machine. Any ideas what could cause this behavior?

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• Can anyone tell why Wordpress is adding this p tag?

  - by Elliott Samuel Lemberger

  Here's the page: http://www.gammagoochee.com/media/ WP is adding a p tag on line 55 between the end of my header and the beginning of my post content. I am using Raw HTML Pro, and the post starts with content surrounded by [raw] tags. There is no content between the last tag in my header, and the beginning of my post. This doesn't happen on my other site pages, and the only difference is that this page is using a template, but the template is the same in this part of the page. All the template does differently than the other site pages is add a sidebar. Anyone have any ideas whatsoever why WP is adding this p tag, and/or how I can prevent it? Thanks so much!

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• ' \r ' vs ' \n ' in C

  - by MCP

  I'm writing a function that basically waits for the user to hit "enter" and then does something. What I've found that works when testing is the below: #include <stdio.h> int main() { int x = getc(stdin); if (x == '\n') { printf("carriage return"); printf("\n"); } else { printf("missed it"); printf("\n"); } } The question I have, and what I tried at first was to do: "if (x == '\r')" but in testing, the program didn't catch me hitting enter. The '\n' seems to correspond to me hitting enter from the console. Can someone explain the difference? Also, to verify, writing it as "if... == "\n"" would mean the character string literal? Ie the user would literally have to enter "\n" from the console, correct? Thanks!

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• receiving OPTIONS instead of GET requests?

  - by Urs

  Hi, all I want to achieve is to implement a servlet providing a json feed for my fullcalendar application. When I inspect http://arshaw.com/js/fullcalendar/examples/json.html with Bugzilla, I see that GET-requests are sent to receive the json feed. However, when I use this example within my scenario, fullcalendar seems to send OPTIONS-requests. The only difference is that I replaced "events: "json-events.php" with "http://localhost:8080/CalendarServletTest/HelloWorldServlet" (the url of my servlet). What do I miss? or is this really a bug?

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• Can I use .NET 4 Code Contracts and remain compatible with .NET 3.5?

  - by mafutrct

  .NET 4 introduced Code Contracts as a new feature. I'd like to use CC, but provide files that can still run in 3.5 SP1. Is that possible? Can I only use parts of the new functionality? Apparently it is possible to have CC only do static checks without being included in the binary files, is that correct? I'm aware CC was available for 3.5 as separate module, is this a feasible workaround in case I can't use the 4 version of CC? Is there a difference in the feature set?

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• What is the role of `while`-loops in computation expressions in F#?

  - by MizardX

  If you define a While method of the builder-object, you can use while-loops in your computation expressions. The signature of the While method is: member b.While (predicate:unit->bool, body:M<'a>) : M<'a> For comparison, the signature of the For method is: member b.For (items:seq<'a>, body:unit->M<'a>) : M<'a> You should notice that, in the While-method, the body is a simple type, and not a function as in the For method. You can embed some other statements, like let and function-calls inside your computation-expressions, but those can impossibly execute in a while-loop more than once. builder { while foo() do printfn "step" yield bar() } Why is the while-loop not executed more than once, but merely repeated? Why the significant difference from for-loops? Better yet, is there some intended strategy for using while-loops in computation-expressions?

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• Problem with loop MATLAB

  - by Jessy

  no time scores 1 10 123 2 11 22 3 12 22 4 50 55 5 60 22 6 70 66 . . . . . . n n n Above a the content of my txt file (thousand of lines). 1st column - number of samples 2nd column - time (from beginning to end ->accumulated) 3rd column - scores I wanted to create a new file which will be the total of every three sample of the scores divided by the time difference of the same sample. e.g. (123+22+22)/ (12-10) = 167/2 = 83.5 (55+22+66)/(70-50) = 143/20 = 7.15 new txt file 83.5 7.15 . . . n so far I have this code: fid=fopen('data.txt') data = textscan(fid,'%*d %d %d') time = (data{1}) score= (data{2}) for sample=1:length(score) ..... // I'm stucked here .. end ....

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• How to print all rows in one page with Crystal Reports

  - by Matt

  I am using Crystal Reports 2011. I am totally new to crystal reports and reporting tools in general. I just added my data fields to the details section, but instead of showing all the rows in one page, a new page is created for each row. I did not use any grouping or change the section paging settings. This only happens for a blank report, when using the report wizard it works fine, but I can't see the difference between what I did and what the report wizard did.

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• SqlDataAdapter.Fill suddenly taking a long time

  - by WraithNath

  I have an application with a central DataTier that can execute a query to a data table using an SQLDataAdapter. None of this code has changed but now all queries are taking at least 10x as long to execute a query returning even one record. The only difference is that I have been using the app in a VM but the issue has started mid way through using the application. eg, the speed issue has not manifested itself from the start of using the VM, rather half way through. Has anyone else had an issue with the SQL Data Adapter taking a long time to fill for no reason? executing the query in Management studio it runs in less than a second. Firewalls are disabled

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• String translation to Portuguese

  - by xrx215

  I wanted to translate strings groupbytext, show in groups in the column menu of a grid panel. In ext-lang-pt.js the string are not included. wheres as in other languages thse string are included. These strings are in cluded in ext-lang-pt_PT.js. what is the difference between ext-lang-pt.js and ext-lang-pt_PT.js. Do I have to include the file ext-lang-pt_PT.js in order to translate the strings in portugese? Please let me know

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• count(*) vs count(column-name) - which is more correct?

  - by bread

  Does it make a difference if you do count(*) vs count(column-name) as in these two examples? I have a tendency to always write count(*) because it seems to fit better in my mind with the notion of it being an aggregate function, if that makes sense. But I'm not sure if it's technically best as I tend to see example code written without the * more often than not. count(*): select customerid, count(*), sum(price) from items_ordered group by customerid having count(*) > 1; vs. count(column-name): SELECT customerid, count(customerid), sum(price) FROM items_ordered GROUP BY customerid HAVING count(customerid) > 1;

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• DocumentBuilder.parse() / Parsing Entities

  - by stormin986

  I'm new to parsing XML and am having an issue with entities. (Am doing this on Android, if it makes a difference). Is there a way to have it turn an entity into the character it represents? I have this in the child of an element: "isn&#39;t" (minus quotes). I would prefer it parse it and the end result be a single text node. However, right now this is turned in to TEXT, ENTITY, TEXT. Is there a way to automatically have it parse the entity into text, or a manual way to do it?

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• PHP strtotime() setting date to default

  - by Paddyd

  I have a script which is reading values from an excel sheet and inserting them into an sql table. My problem is when the script reads in some of the date fields it is setting them to a default value : 1970-01-01 01:00:00 I have noticed that this is happening when it comes across a date where the 'day' is greater than 12 : 13/05/2012 18:52:33 (dd-mm-yyyy hh-mm-ss) I thought this may be due to the script thinking that this is the month field (i.e american format) and it sees it as an invalid value, so I set the default timezone to my own hoping it may resolve the problem but it made no difference. date_default_timezone_set('Europe/Dublin'); Here is an example of what my code is doing: Excel field value : 01/05/2012 18:32:45 Script: $start_time = $data->val($x,5); echo $start_time = date("Y-m-d H:i:s", strtotime($start_time)); Output: 2012-01-05 18:32:45 This is the exact format I am looking for (except for the fact that the day and month fields are switched around i.e american date format) but it doesnt work for the type of dates I mentioned above.

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• C++: need indexed set

  - by user231536

  I need an indexed associative container that operates as follows: initially empty, size=0. when I add a new element to it, it places it at index [size], very similar to a vector's push_back. It increments the size and returns the index of the newly added element. if the element already exists, it returns the index where it occurs. Set seems the ideal data structure for this but I don't see any thing like getting an index from a find operation. Find on a set returns an iterator to the element. Will taking the difference with set.begin() be the correct thing to do in this situation?

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