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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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  • 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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  • 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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  • 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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  • 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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  • In CSS, can "#footer #caption" coexist with "#content # caption"?

    - by Jian Lin
    I was going to "nest" the CSS ids like this #content #caption { color: teal } ... #footer #caption { margin: 2em 1em } because that's the way SASS (a CSS generator) can do nesting for... but then in one HTML document, we cannot have two ids with the same name, isn't that true, so the above nesting won't work or won't work well. (esp if document.getElementById() or $('#caption') or $('caption') is needed to select the element). We can use #content #content_caption { color: teal } ... #footer #footer_caption { margin: 2em 1em } but then why 1 more level of nesting? why not just #content_caption { color: teal } ... #footer_caption { margin: 2em 1em } ?

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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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  • 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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  • What is the exact rule of jQuery's animate() parameters?

    - by Jian Lin
    jQuery 1.4.2's animate() API spec is .animate( properties, [ duration ], [ easing ], [ callback ] ) but it seems that we can supply duration, callback, and no easing .animate({left: '+= 100'}, 600, doThis) and it will work. But if we supply easing and callback and no duration .animate({left: '+=100'}, 'swing', doThis) then the easing won't be taken into effect. So what exactly is the API supposed to be?

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  • An exception to avoid copy and paste code?

    - by Jian Lin
    There are many files in our project that would call a Facebook api. And the call is complicated, spanning usually 8 lines or more, just for the argument values. In this case, we can make it into a function, and place that function in a common_library.php, but doing so would just change the name of the function call from the Facebook API function to our name, and we still need to repeat the 8 lines of arguments. Each time, the call is very similar, but with slight variations to the argument values. In that case, would copy and paste be needed no matter what we do?

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  • What is a SQL statement that can tally up the counts even including the Zeros? (all in 1 statement)

    - by Jian Lin
    A SQL statement can give a list of the most popular gifts that are sent in a Social application, all the way to the ones that are sent 1, or 2 times, but it won't include the Zeros. I think the same goes for getting the list of the most popular Classes that students are registering for, when the registration process for all students is 10 days and now it is the 3rd day. Again, we get the count but the Zeros are not there. Is there a simple SQL statement that can show the whole list, including the zeros?

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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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  • In MVC framworks (such as Ruby on Rails), does usually Model spell as singular and controller and vi

    - by Jian Lin
    I usually see Ruby on Rails books using script/generate model Story name:string link:string which is a singular Story, while when it is controller script/generate controller Stories index then the Story now is Stories, which is plural. Is this a standard on Ruby on Rails? Is it true in other MVC frameworks too, like CakePHP, Symfony, Django, or TurboGears? I see that in the book Rails Space, the controller is also called User, which is the same as the model name, and it is the only exception I see. Update: also, when scaffold is done on Ruby on Rails, then automatically, the model is singular and the controller and view are both plural.

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  • In SQL / MySQL, what is the difference between "On" and "Where" in a join statement?

    - by Jian Lin
    The following statements give the same result (one is using "on", and the other using "where"): mysql> select * from gifts INNER JOIN sentGifts on gifts.giftID = sentGifts.giftID; mysql> select * from gifts INNER JOIN sentGifts where gifts.giftID = sentGifts.giftID; I can only see in a case of a Left Outer Join finding the "unmatched" cases: (to find out the gifts that were never sent by anybody) mysql> select name from gifts LEFT OUTER JOIN sentgifts on gifts.giftID = sentgifts.giftID where sentgifts.giftID IS NULL; In this case, it is first using "on", and then "where". Does the "on" first do the matching, and then "where" does the "secondary" filtering? Or is there a more general rule of using "on" versus "where"? Thanks.

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  • Can GIT, Mercurial, SVN, or other version control tools work well when project tree has binary files

    - by Jian Lin
    Sometimes our project tree can have binary files, such as jpg, png, doc, xls, or pdf. Can GIT, Mercurial, SVN, or other tools do a good job when only part of a binary file is changed? For example, if the spec is written in .doc and it is part of the repository, then if it is 4MB, and edited 100 times but just for 1 or 2 lines, and checked in 100 times during the year, then it is 400MB. If it is 100 different .doc and .xls files, then it is 40GB... not a size that is easy to manage. I have tried GIT and Mercurial and see that they both seem to add a big size of data even when 1 line is changed in a .doc or .pdf. Is there other way inside of GIT or Mercurial or SVN that can do the job?

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  • Expanding Git SHA1 information into a checkin without archiving?

    - by Tim Lin
    Is there a way to include git commit hashes inside a file everytime I commit? I can only find out how to do this during archiving but I haven't been able to find out how to do this for every commit. I'm doing scientific programming with git as revision control, so this kind of functionality would be very helpful for reproducibility reasons (i.e., have the git hash automatically included in all result files and figures).

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  • What are some useful SQL statements that should be known by all developers who may touch the Back en

    - by Jian Lin
    What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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  • What are some useful SQL statements / usage patterns that should be known by all developers who may

    - by Jian Lin
    What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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  • How to change a primary key in SQL to auto_increment?

    - by Jian Lin
    I have a table in MySQL that has a primary key: mysql> desc gifts; +---------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------+-------------+------+-----+---------+-------+ | giftID | int(11) | NO | PRI | NULL | | | name | varchar(80) | YES | | NULL | | | filename | varchar(80) | YES | | NULL | | | effectiveTime | datetime | YES | | NULL | | +---------------+-------------+------+-----+---------+-------+ but I wanted to make it auto_increment. The following statement failed. How can it be modified so that it can work? thanks mysql> alter table gifts modify giftID int primary key auto_increment; ERROR 1068 (42000): Multiple primary key defined

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