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  • In SQL, a Join is actually an Intersection? And it is also a linkage or a "Sideway Union"?

    - by Jian Lin
    I always thought of a Join in SQL as some kind of linkage between two tables. For example, select e.name, d.name from employees e, departments d where employees.deptID = departments.deptID In this case, it is linking two tables, to show each employee with a department name instead of a department ID. And kind of like a "linkage" or "Union" sideway". But, after learning about inner join vs outer join, it shows that a Join (Inner join) is actually an intersection. For example, when one table has the ID 1, 2, 7, 8, while another table has the ID 7 and 8 only, the way we get the intersection is: select * from t1, t2 where t1.ID = t2.ID to get the two records of "7 and 8". So it is actually an intersection. So we have the "Intersection" of 2 tables. Compare this with the "Union" operation on 2 tables. Can a Join be thought of as an "Intersection"? But what about the "linking" or "sideway union" aspect of it?

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  • In SQL, why is "select *, count(*) from sentGifts group by whenSent;" ok, but when "*" and "count(*)

    - by Jian Lin
    In SQL, using the table: mysql> select * from sentGifts; +--------+------------+--------+------+---------------------+--------+ | sentID | whenSent | fromID | toID | trytryWhen | giftID | +--------+------------+--------+------+---------------------+--------+ | 1 | 2010-04-24 | 123 | 456 | 2010-04-24 01:52:20 | 100 | | 2 | 2010-04-24 | 123 | 4568 | 2010-04-24 01:56:04 | 100 | | 3 | 2010-04-24 | 123 | NULL | NULL | 1 | | 4 | 2010-04-24 | NULL | 111 | 2010-04-24 03:10:42 | 2 | | 5 | 2010-03-03 | 11 | 22 | 2010-03-03 00:00:00 | 6 | | 6 | 2010-04-24 | 11 | 222 | 2010-04-24 03:54:49 | 6 | | 7 | 2010-04-24 | 1 | 2 | 2010-04-24 03:58:45 | 6 | +--------+------------+--------+------+---------------------+--------+ 7 rows in set (0.00 sec) The following is OK: mysql> select *, count(*) from sentGifts group by whenSent; +--------+------------+--------+------+---------------------+--------+----------+ | sentID | whenSent | fromID | toID | trytryWhen | giftID | count(*) | +--------+------------+--------+------+---------------------+--------+----------+ | 5 | 2010-03-03 | 11 | 22 | 2010-03-03 00:00:00 | 6 | 1 | | 1 | 2010-04-24 | 123 | 456 | 2010-04-24 01:52:20 | 100 | 6 | +--------+------------+--------+------+---------------------+--------+----------+ 2 rows in set (0.00 sec) But suppose we want the count(*) to appear as the first column: mysql> select count(*), * from sentGifts group by whenSent; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '* from sentGifts group by whenSent' at line 1 it gave an error. Why is it so and what is a way to fix it? I realized that this is ok: mysql> select count(*), whenSent from sentGifts group by whenSent; +----------+------------+ | count(*) | whenSent | +----------+------------+ | 1 | 2010-03-03 | | 6 | 2010-04-24 | +----------+------------+ 2 rows in set (0.00 sec) but what about the one above that gave an error? thanks.

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  • In Ruby, how to write a method to display any object's instance variable names and its values

    - by Jian Lin
    Given any object in Ruby (on Rails), how can I write a method so that it will display that object's instance variable names and its values, like this: @x: 1 @y: 2 @link_to_point: #<Point:0x10031b298 @y=20, @x=38> I also want to be able to print <br> to the end of each instance variable's value so as to print them out nicely on a webpage. the difficulty now seems to be that not every instance variable has an accessor, so it can't be called with obj.send(var_name) (the var_name has the "@" removed, so "@x" becomes "x")

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  • If the "with" statement in Javascript creates a new scope, why does the following code not work as e

    - by Jian Lin
    If the "with" statement in Javascript creates a new scope, shouldn't clicking on the links show a different x which are in different scopes? It doesn't. <a href="#" id="link1">ha link 1</a> <a href="#" id="link2">ha link 2</a> <a href="#" id="link3">ha link 3</a> <a href="#" id="link4">ha link 4</a> <a href="#" id="link5">ha link 5</a> <script type="text/javascript"> for (i = 1; i <= 5; i++) { with({foo:"bar"}) { var x = i; document.getElementById('link' + i).onclick = function() { alert(x); return false; } } } </script>

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  • why assert_equal() in Ruby on Rails sometimes seem to compare by Identity and sometimes by value?

    - by Jian Lin
    it was very weird that yesterday, I was do an integration test in Rails and assert_equal array_of_obj1, array_of_obj2 # obj1 from db, obj2 created in test and it failed. The values shown inside the array and objects were identical. If I change the test to assert array_of_obj1 == array_of_obj2 Then it will pass. But today, the first test actually passed. What reason could it be? Is assert_equal always using == or .equal? in Rails 2.2 or 2.3.5?

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  • Using Git or Mercurial, how would you know when you do a clone or a pull, no one is checking in file

    - by Jian Lin
    Using Git or Mercurial, how would you know when you do a clone or a pull, no one is checking in files (pushing it)? It can be important that: 1) You never know it is in an inconsistent state, so you try for 2 hours trying to debug the code for what's wrong. 2) With all the framework code -- potentially hundreds of files -- if some files are inconsistent with the other, can't the rake db:migrate or script/generate controller cause some damage or inconsistencies to the code base?

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  • Dec 5th Links: ASP.NET, ASP.NET MVC, jQuery, Silverlight, Visual Studio

    - by ScottGu
    Here is the latest in my link-listing series.  Also check out my VS 2010 and .NET 4 series for another on-going blog series I’m working on. [In addition to blogging, I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu] ASP.NET ASP.NET Code Samples Collection: J.D. Meier has a great post that provides a detailed round-up of ASP.NET code samples and tutorials from a wide variety of sources.  Lots of useful pointers. Slash your ASP.NET compile/load time without any hard work: Nice article that details a bunch of optimizations you can make to speed up ASP.NET project load and compile times. You might also want to read my previous blog post on this topic here. 10 Essential Tools for Building ASP.NET Websites: Great article by Stephen Walther on 10 great (and free) tools that enable you to more easily build great ASP.NET Websites.  Highly recommended reading. Optimize Images using the ASP.NET Sprite and Image Optimization Framework: A nice article by 4GuysFromRolla that discusses how to use the open-source ASP.NET Sprite and Image Optimization Framework (one of the tools recommended by Stephen in the previous article).  You can use this to significantly improve the load-time of your pages on the client. Formatting Dates, Times and Numbers in ASP.NET: Scott Mitchell has a great article that discusses formatting dates, times and numbers in ASP.NET.  A very useful link to bookmark.  Also check out James Michael’s DateTime is Packed with Goodies blog post for other DateTime tips. Examining ASP.NET’s Membership, Roles and Profile APIs (Part 18): Everything you could possibly want to known about ASP.NET’s built-in Membership, Roles and Profile APIs must surely be in this tutorial series. Part 18 covers how to store additional user info with Membership. ASP.NET with jQuery An Introduction to jQuery Templates: Stephen Walther has written an outstanding introduction and tutorial on the new jQuery Template plugin that the ASP.NET team has contributed to the jQuery project. Composition with jQuery Templates and jQuery Templates, Composite Rendering, and Remote Loading: Dave Ward has written two nice posts that talk about composition scenarios with jQuery Templates and some cool scenarios you can enable with them. Using jQuery and ASP.NET to Build a News Ticker: Scott Mitchell has a nice tutorial that demonstrates how to build a dynamically updated “news ticker” style UI with ASP.NET and jQuery. Checking All Checkboxes in a GridView using jQuery: Scott Mitchell has a nice post that covers how to use jQuery to enable a checkbox within a GridView’s header to automatically check/uncheck all checkboxes contained within rows of it. Using jQuery to POST Form Data to an ASP.NET AJAX Web Service: Rick Strahl has a nice post that discusses how to capture form variables and post them to an ASP.NET AJAX Web Service (.asmx). ASP.NET MVC ASP.NET MVC Diagnostics Using NuGet: Phil Haack has a nice post that demonstrates how to easily install a diagnostics page (using NuGet) that can help identify and diagnose common configuration issues within your apps. ASP.NET MVC 3 JsonValueProviderFactory: James Hughes has a nice post that discusses how to take advantage of the new JsonValueProviderFactory support built into ASP.NET MVC 3.  This makes it easy to post JSON payloads to MVC action methods. Practical jQuery Mobile with ASP.NET MVC: James Hughes has another nice post that discusses how to use the new jQuery Mobile library with ASP.NET MVC to build great mobile web applications. Credit Card Validator for ASP.NET MVC 3: Benjii Me has a nice post that demonstrates how to build a [CreditCard] validator attribute that can be used to easily validate credit card numbers are in the correct format with ASP.NET MVC. Silverlight Silverlight FireStarter Keynote and Sessions: A great blog post from John Papa that contains pointers and descriptions of all the great Silverlight content we published last week at the Silverlight FireStarter.  You can watch all of the talks online.  More details on my keynote and Silverlight 5 announcements can be found here. 31 Days of Windows Phone 7: 31 great tutorials on how to build Windows Phone 7 applications (using Silverlight).  Silverlight for Windows Phone Toolkit Update: David Anson has a nice post that discusses some of the additional controls provided with the Silverlight for Windows Phone Toolkit. Visual Studio JavaScript Editor Extensions: A nice (and free) Visual Studio plugin built by the web tools team that significantly improves the JavaScript intellisense support within Visual Studio. HTML5 Intellisense for Visual Studio: Gil has a blog post that discusses a new extension my team has posted to the Visual Studio Extension Gallery that adds HTML5 schema support to Visual Studio 2008 and 2010. Team Build + Web Deployment + Web Deploy + VS 2010 = Goodness: Visual blogs about how to enable a continuous deployment system with VS 2010, TFS 2010 and the Microsoft Web Deploy framework.  Visual Studio 2010 Emacs Emulation Extension and VIM Emulation Extension: Check out these two extensions if you are fond of Emacs and VIM key bindings and want to enable them within Visual Studio 2010. Hope this helps, Scott

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  • PHP suddenly failed after IIS update

    - by James Hay
    All my application pools were stopped this morning after I got to work. I can restart them, but when I try to load the website the app pool crashes again. Update: I've looked in the GAC as the error below suggests and it seems that the file is not there. How do I get it back? Update 2: I found a further error in the event log saying The Module name FastCgiModule path C:\WINDOWS\System32\inetsrv\iisfcgi.dll returned an error from registration. The data is the error. So following the information from here http://forums.iis.net/t/1153937.aspx I removed CGI and my sites are working again. This has fixed the initial problem, but now I don't have FastCGI so I'm fairly sure that PHP will no longer be working (I don't have any PHP at the moment to test). Original Post I'm getting this error in the event viewer: IISMANAGER_ERROR_LOADING_PROVIDER_TYPE IIS Manager could not load type 'Web.Management.PHP.PHPProvider, Web.Management.PHP, Version=1.2.0.0, Culture=neutral, PublicKeyToken=8175de49a9aec91d' for module provider 'PHP' that is declared in %windir%\system32\inetsrv\config\administration.config. Verify that the type is correct, and that the assembly that contains the module provider is in the Global Assembly Cache (GAC). Exception:System.IO.FileNotFoundException: Could not load file or assembly 'Web.Management.PHP, Version=1.2.0.0, Culture=neutral, PublicKeyToken=8175de49a9aec91d' or one of its dependencies. The system cannot find the file specified. File name: 'Web.Management.PHP, Version=1.2.0.0, Culture=neutral, PublicKeyToken=8175de49a9aec91d' at System.RuntimeTypeHandle._GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark, Boolean loadTypeFromPartialName) at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark) at System.RuntimeType.PrivateGetType(String typeName, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark) at System.Type.GetType(String typeName, Boolean throwOnError) at Microsoft.Web.Management.Server.AdministrationModuleProvider.GetModuleProvider(String userName, String connectionName) WRN: Assembly binding logging is turned OFF. To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1. Note: There is some performance penalty associated with assembly bind failure logging. To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog]. Process:InetMgr Connection:CT211511\Administrator Everything was working fine last night when I left work, and since they've done the maintenance it's all broken.

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  • Excel error "This workbook contains Excel 4.0 macros or Excel 5.0 modules"

    - by James
    I have a workbook that was protected via the Protect Workbook feature. It was sent to someone else to modify. When they sent it back, it was unprotected and when I try to reprotect it I get this error, "This workbook contains Excel 4.0 macros or Excel 5.0 modules. If you would like to password protect or restrict permission to this document, you need to remove these macros." I looked and there are no new macros in the edited file. The original file contained the same macros and it was able to be write protected, so I'm not sure why the modified file is having a problem. What are common causes and solutions for this error and does it make sense for the modified file to have the error when the original doesn't?

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  • Severe errors in solr configuration: Error loading class 'solr.TrieDateField'

    - by James Lawruk
    Installed Solr on my Windows XP PC. Tomcat seems to be working fine. Cannot get Solr to work. I noticed the TrieDateField is declared in a file called schema.xml in the SolrHome directory. Any thoughts? The Url http://localhost:8080/solr/ returns: HTTP Status 500 - Severe errors in solr configuration. Check your log files for more detailed information on what may be wrong. If you want solr to continue after configuration errors, change: false in null ------------------------------------------------------------- org.apache.solr.common.SolrException: Unknown fieldtype 'date' specified on field updated Here is an excerpt from the catalina log file: SEVERE: org.apache.solr.common.SolrException: Error loading class 'solr.TrieDateField' at org.apache.solr.core.SolrResourceLoader.findClass(SolrResourceLoader.java:273) Caused by: java.lang.ClassNotFoundException: solr.TrieDateField

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  • Why does ssh hang after "debug1: loaded 3 keys"

    - by James Moore
    Trying to log in to an Amazon EC2 instance running Ubuntu 10.04.1. I can log in just fine, no issues. A different user, coming from a different network just gets this: OpenSSH_4.3p2, OpenSSL 0.9.8e-fips-rhel5 01 Jul 2008 debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug1: Connecting to xxxx [xxxx] port 80. debug1: Connection established. debug1: identity file /.ssh/identity type -1 debug1: identity file /.ssh/id_rsa type -1 debug1: identity file /.ssh/id_dsa type -1 debug1: loaded 3 keys And then it hangs. We've tried running sshd on port 22 and port 80 I'm guessing that it's not a firewall problem since the verbose output reports that the connection is established. I don't see anything in /var/log/auth.log when the failing user connects. I do see entries when I log in successfully.

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  • How to set ulimits in Solaris 10

    - by James Bradley
    I normally use pam_limits.so and /etc/security/limits.conf to set ulimits on filesize/cputime etc for the regular users logging in to my server running Ubuntu. Can anyone give the best way of doing similar with Solaris 10. I think it is done using /etc/system but have no idea what to add to the file or indeed if it is the correct file. I'm particularly interested in setting up ulimit -f without going down the .profile route.

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