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  • It seems like the safest way to think of an Inner Join is to think of it as a Cross Join and then sa

    - by Jian Lin
    It seems like the safest way to think of an Inner Join is to think of it as a Cross Join and then satisfying some condition(s)? Because the equi-join can be obvious, but the non-equi-join can be a bit confusing. But if we always use the Cross Join, and then filter out the ones satisfying the condition, then we get the resulting table. In other words, we can always analyze it by using the first record on the left table, and then go through every single records on the right, and then repeat that for 2nd record on the left, and for the 3rd, 4th, ... etc. So in our mind, we can analyze it using this way, and it is like O(n^2), although what happens in the DBMS maybe that it is a lot faster (when an index is present). Is there another good way to think of it besides this method?

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  • C++ explicit template specialization of templated constructor of templated class

    - by Victor Liu
    I have a class like template <class T> struct A{ template <class U> A(U u); }; I would like to write an explicit specialization of this for a declaration like A<int>::A(float); In the following test code, if I comment out the specialization, it compiles with g++. Otherwise, it says I have the wrong number of template parameters: #include <iostream> template <class T> struct A{ template <class U> A(T t, U *u){ *u += U(t); } }; template <> template <> A<int>::A<int,float>(int t, float *u){ *u += U(2*t); } int main(){ float f = 0; int i = 1; A<int>(i, &f); std::cout << f << std::endl; return 0; }

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  • Firebug's "net" tab is not showing anything?

    - by Jian Lin
    I usually run Fiddler for net traffic monitoring and now am using a Mac machine. I thought Firebug's net tab can show the traffic that is fetched through AJAX (the net tab is enabled). But if I try google.com, and type in something, its "google suggest" will show a bunch of suggestions, but the Firebug's "net" tab is not showing anything?

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  • Why in Ruby, a || 1 will throw an error when `a` is undefined, but a = a || 1 will not?

    - by Jian Lin
    When a is undefined, then a || 1 will throw an error, but a = a || 1 will not. Isn't that a little bit inconsistent? irb(main):001:0> a NameError: undefined local variable or method `a' for main:Object from (irb):1 from c:/ruby/bin/irb:12:in `<main>' irb(main):002:0> a || 1 NameError: undefined local variable or method `a' for main:Object from (irb):2 from c:/ruby/bin/irb:12:in `<main>' irb(main):003:0> a = a || 1 => 1

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  • Using Mercurial (hg), how to push just one file or one directory out?

    - by Jian Lin
    Using Mercurial, we can commit one file by using hg commit file.rb or 1 folder hg commit foldername But how can we push just 1 file or 1 folder out? The whole project can be pushed using hg push ssh://[email protected]//project/code/preliminary but there seems to be no way to push out just 1 file or 1 folder? I tried the following and they don't work: hg push ssh://[email protected]//project/code/preliminary app/views/index.html.erb or hg push ssh://[email protected]//project/code/preliminary/app/views/index.html.erb

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  • Recreation of DB using "mysql mydb < mydb.sql" is really slow when the table has tens of millions of

    - by Jian Lin
    It seems that a MySQL database that has a table with tens of millions of records will get a big INSERT INTO statement when the following mysqldump some_db > some_db.sql is done to back up the database. (is it 1 insert statement that handles all the records?) So when reconstructing the DB using mysql some_db < some_db.sql then the CPU is hardly busy (about 1.8% usage by the mysql process... I don't see a mysqld either?) and also the hard disk doesn't seem to be too busy... Last time, the whole restore process took 5 hours. Is there a way to make it faster? Such as, when doing mysqldump, can it break the INSERT statement into shorter ones, so that the mysql doesn't need to parse the line so hard when restoring the DB?

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  • How can I modify my classes to use it's collections in WPF TreeView

    - by Victor
    Hello, i'am trying to modify my objects to make hierarchical collection model. I need help. My objects are Good and GoodCategory: public class Good { int _ID; int _GoodCategory; string _GoodtName; public int ID { get { return _ID; } } public int GoodCategory { get { return _GoodCategory; } set { _GoodCategory = value; } } public string GoodName { get { return _GoodName; } set { _GoodName = value; } } public Good(IDataRecord record) { _ID = (int)record["ID"]; _GoodtCategory = (int)record["GoodCategory"]; } } public class GoodCategory { int _ID; string _CategoryName; public int ID { get { return _ID; } } public string CategoryName { get { return _CategoryName; } set { _CategoryName = value; } } public GoodCategory(IDataRecord record) { _ID = (int)record["ID"]; _CategoryName = (string)record["CategoryName"]; } } And I have two Collections of these objects: public class GoodsList : ObservableCollection<Good> { public GoodsList() { string goodQuery = @"SELECT `ID`, `ProductCategory`, `ProductName`, `ProductFullName` FROM `products`;"; using (MySqlConnection conn = ConnectToDatabase.OpenDatabase()) { if (conn != null) { MySqlCommand cmd = conn.CreateCommand(); cmd.CommandText = productQuery; MySqlDataReader rdr = cmd.ExecuteReader(); while (rdr.Read()) { Add(new Good(rdr)); } } } } } public class GoodCategoryList : ObservableCollection<GoodCategory> { public GoodCategoryList () { string goodQuery = @"SELECT `ID`, `CategoryName` FROM `product_categoryes`;"; using (MySqlConnection conn = ConnectToDatabase.OpenDatabase()) { if (conn != null) { MySqlCommand cmd = conn.CreateCommand(); cmd.CommandText = productQuery; MySqlDataReader rdr = cmd.ExecuteReader(); while (rdr.Read()) { Add(new GoodCategory(rdr)); } } } } } So I have two collections which takes data from the database. But I want to use thats collections in the WPF TreeView with HierarchicalDataTemplate. I saw many post's with examples of Hierarlichal Objects, but I steel don't know how to make my objects hierarchicaly. Please help.

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  • Why is the ( ) mandatory in the SQL statement select * from gifts INNER JOIN sentgifts using (giftID

    - by Jian Lin
    Why is the ( ) mandatory in the SQL statement select * from gifts INNER JOIN sentgifts using (giftID); ? The ( ) usually is for specifying grouping of something. But in this case, are we supposed to be able to use 2 or more field names... in the example above, it can be all clear that it is 1 field, is it just that the parser is not made to bypass the ( ) when it is all clear? (such as in the language Ruby).

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  • In Ruby, why is a method invocation not be able to be treated as a unit when "do" and "end" is used?

    - by Jian Lin
    The following question is related to the question "Ruby Print Inject Do Syntax". My question is, can we insist on using do and end and make it work with puts or p? This works: a = [1,2,3,4] b = a.inject do |sum, x| sum + x end puts b # prints out 10 so, is it correct to say, inject is a class method of the Array class, which takes a block of code, and then returns a number. If so, then it should be no different from calling a function and getting back a return value: b = foo(3) puts b or b = circle.getRadius() puts b In the above two cases, we can directly say puts foo(3) puts circle.getRadius() so, there is no way to make it work directly by using the following 2 ways: a = [1,2,3,4] puts a.inject do |sum, x| sum + x end but it gives ch01q2.rb:7:in `inject': no block given (LocalJumpError) from ch01q2.rb:4:in `each' from ch01q2.rb:4:in `inject' from ch01q2.rb:4 grouping the method call using ( ) doesn't work either: a = [1,2,3,4] puts (a.inject do |sum, x| sum + x end) and this gives: ch01q3.rb:4: syntax error, unexpected kDO_BLOCK, expecting ')' puts (a.inject do |sum, x| ^ ch01q3.rb:4: syntax error, unexpected '|', expecting '=' puts (a.inject do |sum, x| ^ ch01q3.rb:6: syntax error, unexpected kEND, expecting $end end) ^ finally, the following version works: a = [1,2,3,4] puts a.inject { |sum, x| sum + x } but why doesn't the grouping of the method invocation using ( ) work in the earlier example? What if a programmer insist that he uses do and end, can it be made to work?

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  • Jetty offline documentation

    - by Victor Sorokin
    Is there any more-or-less comprehensive documentation for Jetty (e.g., similar to Tomcat or, really, in any form)? Theirs online wikis seems to be quite informative, but servers seem to be slow. Maybe, there some way to build docs from Jetty source distribution? I tried mvn site to no avail.

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  • Using Ruby on Rails, can a polymorphic database be created in a few steps (with polymorphic associat

    - by Jian Lin
    I thought it could be created in a few steps but it can't yet: rails poly cd poly ruby script/generate scaffold animal name:string obj_type:string obj_id:integer rake:migrate ruby script/generate scaffold human name:string passportNumber:string rake:migrate ruby script/generate scaffold dog name:string registrationNumber:string rake:migrate and now change app/models/animal.rb to: class Animal < ActiveRecord::Base belongs_to :obj, :polymorphic => true end and run ruby script/server and go to http://localhost:3000 I thought on the server then if I create an Michael, Human, J123456 and then Woofie, Dog, L23456 then the database will have entries in the Dogs table and "Humen" or "Humans" table as well as in the Animals table? But only the Animals table has records, Dogs and "Humen" do not for some reason. Is there some steps missing?

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  • Determining polygon intersection and containment

    - by Victor Liu
    I have a set of simple (no holes, no self-intersections) polygons, and I need to check that they don't intersect each other (one can be entirely contained in another; that is okay). I can check this by simply checking the per-vertex inside-ness of one polygon versus other polygons. I also need to determine the containment tree, which is the set of relationships that say which polygon contains any given polygon. Since no polygon can intersect any other, then any contained polygon has a unique container; the "next-bigger" one. In other words, if A contains B contains C, then A is the parent of B, and B is the parent of C, and we don't consider A the parent of C. The question: How do I efficiently determine the containment relationships and check the non-intersection criterion? I ask this as one question because maybe a combined algorithm is more efficient than solving each problem separately. The algorithm should take as input a list of polygons, given by a list of their vertices. It should produce a boolean B indicating if none of the polygons intersect any other polygon, and also if B = true, a list of pairs (P, C) where polygon P is the parent of child C. This is not homework. This is for a hobby project I am working on.

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  • In HAML on Ruby on Rails, how to use the :sass filter?

    - by Jian Lin
    If using HAML on Ruby on Rails, then :sass #someDiv border: 3px dashed orange won't have any <style> tag around them. and then :css :sass #someDiv border: 3px dashed orange won't kick on the :sass filter, but :css :sass #someDiv border: 3px dashed orange will kick on the :sass filter, but it is outside of the <style> tag. So how can the :sass filter be used?

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  • delete multi-line block of text with internal flag in povray file

    - by Sibo Lin
    I have a pov-ray file, which defines a lot of cylinders and spheres. Sometimes these shapes are defined to have "color@", which makes the povray unrenderable. One solution I've found is to delete the offending cylinders and spheres. So a file that contains this text cylinder { < -0.17623, 0.24511, -0.27947>, < -0.15220, 0.22658, -0.26472>, 0.00716 texture { colorO } } sphere { < -0.00950, 0.00357, 0.00227>, 0.00716 texture { color@ } } cylinder { < -0.00950, 0.00357, 0.00227>, < 0.00327, 0.00169, 0.00108>, 0.00716 texture { color@ } } sphere { < 0.15373, 0.00601, 0.18223>, 0.00716 texture { colorO } } would turn into this text cylinder { < -0.17623, 0.24511, -0.27947>, < -0.15220, 0.22658, -0.26472>, 0.00716 texture { colorO } } sphere { < 0.15373, 0.00601, 0.18223>, 0.00716 texture { colorO } } Is there some way to do this replacement with a shell script? Preferably in tcsh. Thanks!

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  • In Ruby on Rails, routes.rb, if map.something will create something_path and something_url, does map

    - by Jian Lin
    In Ruby on Rails, routes.rb, if we create a "named route" map.something ":a/:b", :controller => 'foobar' it will also create something_path and something_url which are two methods usable in the controller and in the view. Does map.connect create something like that too? Otherwise, isn't map.connect somewhat disadvantaged in this way? I checked that connect_path and connect_url both aren't created automatically.

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  • Load a list of localized strings at once in IOS

    - by Victor Ronin
    I want to show a table with the list of strings which are localized. The straightforward method would be: a) Point data source to my ViewController b) Define an array c) Allocate the array in my ViewController and init (arrayWithObjects) it with the strings from localized resources (NSLocalizedString) d) Use this array in UITableViewDataSource delegated methods Mainly my concern is item b). The construction looks quite heavy and I wonder whether I can somehow specify and load whole list of localized string at once.

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  • Problem in using a second call to send() in C

    - by Paulo Victor
    Hello. Right now I'm working in a simple Server that receives from client a code referring to a certain operation. The server receives this data and send back the signal that it's waiting for the proper data. /*Server Side*/ if (codigoOperacao == 0) { printf("A escolha foi 0\n"); int bytesSent = SOCKET_ERROR; char sendBuff[1080] = "0"; /*Here "send" returns an error msgm while trying to send back the signal*/ bytesSent = send(socketEscuta, sendBuff, 1080, 0); if (bytesSent == SOCKET_ERROR) { printf("Erro ao enviar"); return 0; } else { printf("Bytes enviados : %d\n", bytesSent); char structDesmontada[1080] = ""; bytesRecv = recebeMensagem(socketEscuta, structDesmontada); printf("structDesmontada : %s", structDesmontada); } } Following here is the client code responsible for sending the operation code and receiving the signal char sendMsg[1080] = "0"; char recvMsg[1080] = ""; bytesSent = send(socketCliente, sendMsg, sizeof(sendMsg), 0); printf("Enviei o codigo (%d)\n", bytesSent); /*Here the program blocks in a infinite loop since the server never send anything*/ while (bytesRecv == SOCKET_ERROR) { bytesRecv = recv(socketCliente, recvMsg, 1080, 0); if (bytesRecv > 0) { printf("Recebeu\n"); } Why this is happening only in the second attempt to send some data? Because the first call to send() works fine. Hope someone can help!! Thnks

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  • How to use a data type (table) defined in another database in SQL2k8?

    - by Victor Rodrigues
    I have a Table Type defined in a database. It is used as a table-valued parameter in a stored procedure. I would like to call this procedure from another database, and in order to pass the parameter, I need to reference this defined type. But when I do DECLARE @table dbOtherDatabase.dbo.TypeName , it tells me that The type name 'dbOtherDatabase.dbo.TypeName' contains more than the maximum number of prefixes. The maximum is 1. How could I reference this table type?

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  • Standard and reliable mouse-reporting with GLUT

    - by Victor
    Hello! I'm trying to use GLUT (freeglut) in my OpenGL application, and I need to register some callbacks for mouse wheel events. I managed to dig out a fairly undocumented function: api documentation But the man page and the API entry for this function both state the same thing: Note: Due to lack of information about the mouse, it is impossible to implement this correctly on X at this time. Use of this function limits the portability of your application. (This feature does work on X, just not reliably.) You are encouraged to use the standard, reliable mouse-button reporting, rather than wheel events. Fair enough, but how do I use this standard, reliable mouse-reporting? And how do I know which is the standard? Do I just use glutMouseFunc() and use button values like 4 and 5 for the scroll up and down values respectively, say if 1, 2 and 3 are the left, middle and right buttons? Is this the reliable method? Bonus question: it seems the `xev' tool is reporting different values for my buttons. My mouse buttons are numbered from 1 to 5 with xev, but glut is reporting buttons from 0 to 4, i.e. an off-by-one. Is this common?

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  • is there a rule in CSS that says class="one two" vs class="two one" and the second will override the

    - by Jian Lin
    Right now, there seems to be no such effect. Example: both divs are orange in color on Firefox <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <style> .one { border: 6px dashed green } .two { border: 6px dashed orange } </style> </head> <body> <div class="one two"> hello world </div> <div class="two one"> hello world </div>

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  • Why does it matter that in Javascript, scope is function-level, not block-level?

    - by Jian Lin
    In the question http://stackoverflow.com/questions/1451009/javascript-infamous-loop-problem the accepted answer from Christoph's says that JavaScript's scopes are function-level, not block-level What if Javascript's scopes are block-level, then would the Infamous Loop problem still occur? But will there be a different (or easier way) to fix it? Is it as opposed to other languages, where using a { would start a new scope?

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  • Javascript code works only when the page loads

    - by victor
    I have a page with a dropdown and two textboxes. The javascript code checks to make sure that if the dropdown says Appointment Made or Patient Scheduled, the appropriate text boxes will have dates in them. When the page loads and the drop down shows either of the two above, all works fine but when I change the drop down the script does not work. I have put an alert statament after the third line and do see that when I make a change to patient_status, the variable a gets updated but for some reason the script fails and does not prompt. For example if the page loads and Appointment Made is selected, the script will prompt, but if I change the drop down to Patient Scheduled, it will not prompt. Thank You. function calculate() { a= document.getElementById("EditRecordpatient_status").value; b= document.getElementById("EditRecordSurgery_Date").value; c= document.getElementById("EditRecordConsult_Date").value; alert(a); alert(b); alert(c); if (a=="Appointment Made" && c=="") { alert('You have scheduled a patient for consultation but the consult date is missing!'); return false; } else if (a=="Patient Scheduled" && b=="") { alert('You have scheduled a patient for surgery but the surgery date is missing!'); return false; } else { return true; } } document.getElementById("Mod0EditRecord").onclick=calculate;

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  • Problem with notification bar in fullscreen app

    - by Mathias Lin
    I run an app in fullscreen mode where fullscreen is defined as a theme in xml for the entire app. <style name="AskTingTingTheme" parent="android:Theme"> <item name="android:windowNoTitle">true</item> <item name="android:windowFullscreen">true</item> <item name="android:windowBackground">@null</item> </style> Generally it works ok, but there are some issues in some cases: 1) when I open the search dialog via search button - Screenshot: http://tinyurl.com/3xzadft 2) when I open spinner widgets that are very long and fill the screen (so that the list is usually scrollable) - Screenshot: http://tinyurl.com/39q5ya2 The problem is that when I open the search dialog or spinner widget, the system notification bar occurs for a few millisecs and then scrolls off the screen again. Please see the screenshots linked above. I'm currently on 2.2 with NexusOne, but same thing happened on 2.1update1 (esp. case 2) as well before.

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