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

  - 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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• In SQL / MySQL, can a Left Outer Join be used to find out the duplicates when there is no Primary ID

  - by Jian Lin

  I would like to try using Outer Join to find out duplicates in a table: If a table has Primary Index ID, then the following outer join can find out the duplicate names: mysql> select * from gifts; +--------+------------+-----------------+---------------------+ | giftID | name | filename | effectiveTime | +--------+------------+-----------------+---------------------+ | 2 | teddy bear | bear.jpg | 2010-04-24 04:36:03 | | 3 | coffee | coffee123.jpg | 2010-04-24 05:10:43 | | 6 | beer | beer_glass.png | 2010-04-24 05:18:12 | | 10 | heart | heart_shape.jpg | 2010-04-24 05:11:29 | | 11 | ice tea | icetea.jpg | 2010-04-24 05:19:53 | | 12 | cash | cash.png | 2010-04-24 05:27:44 | | 13 | chocolate | choco.jpg | 2010-04-25 04:04:31 | | 14 | coffee | latte.jpg | 2010-04-27 05:49:52 | | 15 | coffee | espresso.jpg | 2010-04-27 06:03:03 | +--------+------------+-----------------+---------------------+ 9 rows in set (0.00 sec) mysql> select * from gifts g1 LEFT JOIN (select * from gifts group by name) g2 on g1.giftID = g2.giftID where g2.giftID IS NULL; +--------+--------+--------------+---------------------+--------+------+----------+---------------+ | giftID | name | filename | effectiveTime | giftID | name | filename | effectiveTime | +--------+--------+--------------+---------------------+--------+------+----------+---------------+ | 14 | coffee | latte.jpg | 2010-04-27 05:49:52 | NULL | NULL | NULL | NULL | | 15 | coffee | espresso.jpg | 2010-04-27 06:03:03 | NULL | NULL | NULL | NULL | +--------+--------+--------------+---------------------+--------+------+----------+---------------+ 2 rows in set (0.00 sec) But what if the table doesn't have a Primary Index ID, then can an outer join still be used to find out duplicates?

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• Can Git or Mercurial be set to bypass the local repository and go straight to the central one?

  - by Jian Lin

  Using Git or Mercurial, if the working directory is 1GB, then the local repository will be another 1GB (at least), residing normally in the same hard drive. And then when pushed to a central repository, there will be another 1GB. Can Git or Mercurial be set to use only a working directory and then a central repository, without having 3 copies of this 1GB data? (actually, when the central repository also update, then there are 4 copies of the same data... can it be reduced? In the SVN scenario, when there are 5 users, then there will be 6GB of data total. With Distributed Version Control, then there will be 12GB of data?)

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• any PHP or Ruby library to convert Tranditional Chinese to Simplified Chinese or vice versa?

  - by Jian Lin

  any PHP or Ruby library to convert Tranditional Chinese to Simplified Chinese or vice versa (Big5 <-- GB)? the iconv library won't do it as it merely convert the encoding -- the glyph stays the same.

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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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• How to build march-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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• How to workaround Python "WindowsError messages are not properly encoded" problem?

  - by Victor Lin

  It's a trouble when Python raised a WindowsError, the encoding of message of the exception is always os-native-encoded. For example: import os os.remove('does_not_exist.file') Well, here we get an exception: Traceback (most recent call last): File "<stdin>", line 1, in <module> WindowsError: [Error 2] ???????????: 'does_not_exist.file' As the language of my Windows7 is Traditional Chinese, the default error message I get is in big5 encoding (as know as CP950). >>> try: ... os.remove('abc.file') ... except WindowsError, value: ... print value.args ... (2, '\xa8t\xb2\xce\xa7\xe4\xa4\xa3\xa8\xec\xab\xfc\xa9w\xaa\xba\xc0\xc9\xae\xd7\xa1C') >>> As you see here, error message is not Unicode, then I will get another encoding exception when I try to print it out. Here is the issue, it can be found in Python issue list: http://bugs.python.org/issue1754 The question is, how to workaround this? How to get the native encoding of WindowsError? The version of Python I use is 2.6. Thanks.

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• Can Ruby on Rails handle AJAX Response by Static Javascript code? by using RJS?

  - by Jian Lin

  So it looks like on RoR, when Ajax (using form_remote_tag) returns a success code, Javascript is also returned to handle the visual effects. (this is the RJS mechanism) using Fiddler, I do see the following response: try { Element.update("vote_score", "Score 58"); $("vote_score").visualEffect("highlight"); } catch (e) { alert('RJS error:\n\n' + e.toString()); alert('Element.update(\"vote_score\", \"Score 58\");\n$(\"vote_score\").visualEffect(\"highlight\");'); throw e } Will there be situation where the code is quite big (like 1 or 2k) that RJS can use some sort of static Javascript already loaded to handle the effect? Is there any other ways to use static Javascript already loaded with the page? Must it be just raw Javascript and use the Prototype's Ajax success response to call the static Javascript code, or can it be some Rails mechanism related to RJS?

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• In SQL / MySQL, are there reasons not to put one-to-one relationship in the same table?

  - by Jian Lin

  One-to-one relationship could usually be stored in the same table. Are there reasons not to store them in the same table?

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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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• For SQL, when did it start to be desirable to always use the words "Inner Join" instead of implicitl

  - by Jian Lin

  For SQL, when did it start to be desirable to always use the words "Inner Join" instead of implicitly joining by: select * from t1, t2 where t1.ID = t2.ID; ? Is it just for style or to distinguish between outer join or are there other reasons for it?

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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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• 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 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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• 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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• 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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• 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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• 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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• is there a way to pipe the GIT or Mercurial diff output to a GUI Diff tool?

  - by Jian Lin

  the diff result in text might be hard to get used to at first. Is there a way to pipe that output to a visual diff tool, such as something like $hg diff --visual code.rb or $ hg diff code.rb | sometool so that the result can be viewed visually?

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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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