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  • If Inner Join can be thought of as Cross Join but filtering out the records satisfying the condition

    - by Jian Lin
    If an Inner Join can be thought of as a cross join and then getting the records that satisfy the condition, then a LEFT OUTER JOIN can be thought of as that, plus ONE record on the left table that doesn't satisfy the condition. In other words, it is not a cross join that "goes easy" on the left records (even when the condition is not satisfied), because then the left record can appear many times (as many as how many records there are in the right table). So the LEFT OUTER JOIN is the Cross JOIN with the records satisfying the condition, plus ONE record from the LEFT TABLE that doesn't satisfy the condition.

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  • ASP.NET custom server control: nested items

    - by Dylan Lin
    Hi, In the aspx code view, we can code like this: <asp:ListBox runat="server"> <asp:ListItem Text="Item1" /> <asp:ListItem Text="Item2" /> </asp:ListBox> However, the ListItem class is not a server control. How could we do that? Is there some attributes being consumed by the visual studio? Thanks:)

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  • sqlcipher command line not working

    - by Min Lin
    I have a encrypted sqlite db and its key. (Which is generated by an android program). However, when I open the db in command line I can not read the db. The command line tool is installed by: brew install sqlcipher I open the database by: sqlcipher EnDB.db >pragma key="6b74fcd"; >select * from bizinfo; It keeps telling me "Error: file is encrypted or is not a database" However, if I open the database file with gui app sqlite database browser (which is a windows program and I run it in wine). It pops up a window for me to enter the key, with 6b74fcd as the key it successfully read the database. As I want to automatically process the db in the future, I can not depend on the GUI. Do you know why the command line is not working?

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  • How to build mach-0 for different architectures?

    - by Victor Lin
    I have some dylibs to load from python with ctypes. I can load libbass.dylib without problem, but I can't load the self-compiled libmp3lame.dylib. Here is the error I get. OSError: dlopen(libmp3lame.dylib, 6): no suitable image found. Did find: libmp3lame.dylib: mach-o, but wrong architecture Then, I inspect the file type of those libs. Here is the result of libbass.dylib: libbass.dylib: Mach-O universal binary with 2 architectures libbass.dylib (for architecture i386): Mach-O dynamically linked shared library i386 libbass.dylib (for architecture ppc): Mach-O dynamically linked shared library ppc And here is the self-compiled one: libmp3lame.dylib: Mach-O 64-bit dynamically linked shared library x86_64 I did compile the lame library with the install instructions: ./configure make make install I'm new to mac system, here comes the problem: how to build the libmp3lame.dylib so that it supports different architecture I want? Thanks.

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  • In Ruby on Rails, why will story.votes return an empty Array object, but story.votes.create will act

    - by Jian Lin
    In Ruby on Rails, say a Story object can "has_many" Vote objects (a story is voted "hot" by many users). So when we do a s = Story.find(:first) s is a Story object, and say s.votes returns [] and s.votes.class returns Array So clearly, s.votes is an empty Array object. At this time, when s.votes.create is called, it actually invokes a method of the Vote class? How come an Array class object can invoke a Vote class method?

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  • PHP cron script with twitter (problem with oauth)

    - by James Lin
    Hi guys, I am trying to write an php twitter script which will be run by crontab, what the script does is to get the tweets from a dedicated twitter account. I have looked at some of the php twitter oauth libraries, all of them seem to use redirect to a twitter page to get a token, then goes back to a callback link. In my case I don't want to have any user interaction at all. Could anyone please tell me what I should do? Regards James

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  • How to get real-time status notification with Facebook SDK via listener

    - by Mathias Lin
    I'm using Twitter4j and the Android Facebook SDK to fetch status messages. With Twitter4J I get real-time notifications whenever a new status has been added to the stream via StatusListener (Twitter4J). In the Facebook SDK I cannot find a similar way, I can only fetch entire streams over and over again in a fixed time interval using RequestListener (Facebook SDK) as far as I see it. Is there any way to get notified of new statuses in realtime with the Facebook SDK in a similar way as with Twitter4J? (Found a similar but unanswered question here: Facebook real-time updated application wall)

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  • In Ruby, how to implement 20 - point and point - 20 using coerce() ?

    - by Jian Lin
    In Ruby, the operation of point - 20 20 - point are to be implemented. But the following code: class Point attr_accessor :x, :y def initialize(x,y) @x, @y = x, y end def -(q) if (q.is_a? Fixnum) return Point.new(@x - q, @y - q) end Point.new(@x - q.x, @y - q.y) end def -@ Point.new(-@x, -@y) end def *(c) Point.new(@x * c, @y * c) end def coerce(something) [self, something] end end p = Point.new(100,100) q = Point.new(80,80) p (-p) p p - q p q - p p p * 3 p 5 * p p p - 30 p 30 - p Output: #<Point:0x2424e54 @x=-100, @y=-100> #<Point:0x2424dc8 @x=20, @y=20> #<Point:0x2424d3c @x=-20, @y=-20> #<Point:0x2424cc4 @x=300, @y=300> #<Point:0x2424c38 @x=500, @y=500> #<Point:0x2424bc0 @x=70, @y=70> #<Point:0x2424b20 @x=70, @y=70> 30 - p will actually be taken as p - 30 by the coerce function. Can it be made to work? I am actually surprise that the - method won't coerce the argument this way: class Fixnum def -(something) if (/* something is unknown class */) a, b = something.coerce(self) return -(a - b) # because we are doing a - b but we wanted b - a, so it is negated end end end that is, the function returns a negated version of a - b instead of just returning a - b.

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  • Does jQuery have a plugin to display a "message bar" like the Twitter "wrong password" bar at the to

    - by Jian Lin
    Twitter will pop down a message bar at the top of the screen say "Wrong password" and after 10 seconds, it will slide up and disappear. Chrome also shows "Do you want to save the password" message box using such a way. Does jQuery have a plug in to do that already? Does it also work in IE 6? Because usually, the display of relative to the viewport (using position: fixed) will not work on IE 6. thanks.

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  • Google groups not finding discussion thread but regular google search does?

    - by Mathias Lin
    I'm having a problem with google groups and finding my own discussion threads. I go to the google group (in my case Android developer group) web view and try to search for my thread by entering the extact title of my thread. But it doesn't appear in the search results. On the other hand, when I search for the same title in the regular google web search, I get the thread right on top of the result list. I thought it might take a while until the groups index all new threads, but still after a few days, it still wouldn't show up. Sample: My thread is here: http://groups.google.com/group/android-developers/browse_thread/thread/0ab41d5056a25ce7 Doing a search for it in Google groups (will give one result, but not mine): http://groups.google.com/group/android-developers/search?group=android-developers&q=Strange+behaviour+with+mediaplayer+and+seekTo&qt_g=Search+this+group Search in Google web search (shows my thread as first result): http://www.google.de/search?sourceid=chrome&ie=UTF-8&q=Strange+behaviour+with+mediaplayer+and+seekTo

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  • Can a binary tree or tree be always represented in a Database as 1 table and self-referencing?

    - by Jian Lin
    I didn't feel this rule before, but it seems that a binary tree or any tree (each node can have many children but children cannot point back to any parent), then this data structure can be represented as 1 table in a database, with each row having an ID for itself and a parentID that points back to the parent node. That is in fact the classical Employee - Manager diagram: one boss can have many people under him... and each person can have n people under him, etc. This is a tree structure and is represented in database books as a common example as a single table Employee.

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  • Can MySQL / SQL's short hand of "Using" be used without saying "Inner Join" ?

    - by Jian Lin
    The following 2 statements are to join using gifts.giftID = sentgifts.giftID: mysql> select * from gifts, sentgifts using (giftID); 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 'using (giftID)' at line 1 and the second one: mysql> select * from gifts INNER JOIN sentgifts using (giftID); +--------+------------+----------------+---------------------+--------+------------+--------+------+---------------------+ | giftID | name | filename | effectiveTime | sentID | whenSent | fromID | toID | trytryWhen | +--------+------------+----------------+---------------------+--------+------------+--------+------+---------------------+ | 2 | teddy bear | bear.jpg | 2010-04-24 04:36:03 | 4 | 2010-04-24 | NULL | 111 | 2010-04-24 03:10:42 | | 6 | beer | beer_glass.png | 2010-04-24 05:18:12 | 5 | 2010-03-03 | 11 | 22 | 2010-03-03 00:00:00 | | 6 | beer | beer_glass.png | 2010-04-24 05:18:12 | 6 | 2010-04-24 | 11 | 222 | 2010-04-24 03:54:49 | | 6 | beer | beer_glass.png | 2010-04-24 05:18:12 | 7 | 2010-04-24 | 1 | 2 | 2010-04-24 03:58:45 | +--------+------------+----------------+---------------------+--------+------------+--------+------+---------------------+ 4 rows in set (0.00 sec) Can the first statement also use the "using" shorthand? It seems that when it is used then the word "Inner Join" must be specified... but the first statement is actually an inner join?

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  • In Ruby, can the coerce() method know what operator it is that requires the help to coerce?

    - by Jian Lin
    In Ruby, it seems that a lot of coerce() help can be done by def coerce(something) [self, something] end that's is, when 3 + rational is needed, Fixnum 3 doesn't know how to handle adding a Rational, so it asks Rational#coerce for help by calling rational.coerce(3), and this coerce instance method will tell the caller: # I know how to handle rational + something, so I will return you the following: [self, something] # so that now you can invoke + on me, and I will deal with Fixnum to get an answer So what if most operators can use this method, but not when it is (a - b) != (b - a) situation? Can coerce() know which operator it is, and just handle those special cases, while just using the simple [self, something] to handle all the other cases where (a op b) == (b op a) ? (op is the operator).

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  • Is using Natural Join or Implicit column names not a good practice when writing SQL in a programming

    - by Jian Lin
    When we use Natural Join, we are joining the tables when both table have the same column names. But what if we write it in PHP and then the DBA add some more fields to both tables, then the Natural Join can break? The same goes for Insert, if we do a insert into gifts values (NULL, "chocolate", "choco.jpg", now()); then it will break the code as well as contaminating the table when the DBA adds some fields to the table (example as column 2 or 3). So it is always best to spell out the column names when the SQL statements are written inside a programming language and stored in a file in a big project.

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  • Programmatically controlled virtual drive

    - by Robert Lin
    How would I go about creating a virtual drive with which I can programmatically and dynamically change the contents? For instance, program A starts running and creates a virtual drive. When program B looks in the drive, it sees an error log and starts reading/processing it. In the middle of all this program A gets a signal from somewhere and decides to add to the log. I want program B to be unaware of the change and just keep on going. Program B should continue reading as if nothing happened. Program A would just report a rediculously large file size for the log and then fill it in as appropriate. Program A would fill the log with tags if program B tries to read past the last entry. I know this is a weird request but there's really no other way to do this... I basically can't rewrite program B so I need to fool it. How do I do this in windows? How about OSX?

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  • In SQL, in what situation do we want to Index a field in a table, or 2 fields in a table at the same

    - by Jian Lin
    In SQL, it is obvious that whenever we want to do a search on millions of record, say CustomerID in a Transactios table, then we want to add an index for CustomerID. Is another situation we want to add an index to a field when we need to do inner join or outer join using that field as a criteria? Such as Inner join on t1.custumerID = t2.customerID. Then if we don't have an index on customerID on both tables, we are looking at O(n^2) because we need to loop through the 2 tables sequentially. If we have index on customerID on both tables, then it becomes O( (log n) ^ 2 ) and it is much faster. Any other situation where we want to add an index to a field in a table? What about adding index for 2 fields combined in a table. That is, one index, for 2 fields together?

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  • Multiple CSS Classes: Properties Overlapping based on the order defined.

    - by Jian Lin
    Is there a rule in CSS that determines the cascading order when multiple classes are defined on an element? (class="one two" vs class="two one") 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 single textarea mess all following xhtml?

    - by Victor Lin
    I encounter a problem in my web program. I got a textarea in my form, sometimes there is nothing in textarea, so genshi template engine just output it as <textarea xxxx /> and here comes the problem, all following tags are in the textarea. Why all browser can't handle single textarea correctly? If I write it as <textarea xxxx></textarea> and everything works fine. Why a single textarea messes following tags in xhtml?

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  • How to implement a link that can get bonus for 5 times by different people on a Social Network?

    - by Jian Lin
    How can we generate a link that can be clicked on by 5 different people on a Social Network game, so that each of the five people can get a bonus? The link will be published as a "newsfeed" on the Social Network such as Facebook. The link shouldn't be easily "generated" by any people as a cheating method. Also, what database table(s) should be added to handle: 1) the bonus can be claimed up to 5 times 2) must be claimed by different people ?

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  • How can this closure test be written in other languages?

    - by Jian Lin
    I wonder how the following closure test can be written in other languages, such as C and Java. Can the same result be expected also in Perl, Python, and PHP? Ideally, we don't need to make a new local variable such as x and assign it the value of i inside the loop, but just so that i has a new copy in the new scope each time. (if possible). (some discussion is in this question.) The following is in Ruby, the "1.8.6" on the first line of result is the Ruby version which can be ignored. p RUBY_VERSION $foo = [] (1..5).each do |i| $foo[i] = lambda { p i } end (1..5).each do |j| $foo[j].call() end the print out is: [MacBook01:~] $ ruby scope.rb "1.8.6" 1 2 3 4 5 [MacBook01:~] $ Contrast that with another test, with i defined outside: p RUBY_VERSION $foo = [] i = 0 (1..5).each do |i| $foo[i] = lambda { p i } end (1..5).each do |j| $foo[j].call() end the print out: [MacBook01:~] $ ruby scope2.rb "1.8.6" 5 5 5 5 5 [MacBook01:~] $

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  • In Ruby, how does coerce() actually work?

    - by Jian Lin
    It is said that when we have a class Point and knows how to perform point * 3 like the following: class Point def initialize(x,y) @x, @y = x, y end def *(c) Point.new(@x * c, @y * c) end end point = Point.new(1,2) p point p point * 3 Output: #<Point:0x336094 @x=1, @y=2> #<Point:0x335fa4 @x=3, @y=6> but then, 3 * point is not understood: Point can't be coerced into Fixnum (TypeError) So we need to further define an instance method coerce: class Point def coerce(something) [self, something] end end p 3 * point Output: #<Point:0x3c45a88 @x=3, @y=6> So it is said that 3 * point is the same as 3.*(point) that is, the instance method * takes an argument point and invoke on the object 3. Now, since this method * doesn't know how to multiply a point, so point.coerce(3) will be called, and get back an array: [point, 3] and then * is once again applied to it, is that true? point * 3 which is the same as point.*(3) and now, this is understood and we now have a new Point object, as performed by the instance method * of the Point class. The question is: 1) who invokes point.coerce(3) ? Is it Ruby automatically, or is it some code inside of * method of Fixnum by catching an exception? Or is it by case statement that when it doesn't know one of the known types, then call coerce? 2) Does coerce always need to return an array of 2 elements? Can it be no array? Or can it be an array of 3 elements? 3) And is the rule that, the original operator (or method) * will then be invoked on element 0, with the argument of element 1? (element 0 and element 1 are the two elements in that array returned by coerce) Who does it? Is it done by Ruby or is it done by code in Fixnum? If it is done by code in Fixnum, then it is a "convention" that everybody follows when doing a coerce? So could it be the code in * of Fixnum do something like this: if (something.typeof? ...) else if ... # other type else if ... # other type else # if it is not a type I know array = something.coerce(self) return array[0].*(array[1]) end

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