SEARCH KEYWORD -- Big data


  Select top 3 values from each group in a table with SQL

Yesterday, my friend Liu Bing asked me a question about how to select top 3 values for each person in a database table using SQL. I think this question is interesting and it deserves some thoughts. Here I record down how to solve this issue. Assume we have a table which has two columns, one column contains the names of some people and the other column contains some values related to each person. One person can have more than one value. Each value has a numeric type. The question is we want to se...

   SQL,Correlated query,top 3     2013-05-23 03:21:25

  Guide to use Compass

Sass is one kind of CSS Preprocessor, it can make CSS development simple and maintainable. But to show its real power we may need to have Compass. This article is to introduce Compass. Once you learn Compass, your CSS development efficiency will be largely improved. Here we assume you have mastered the major uses of CSS, if you know Sass, then it's better. It's still ok if you don't know Sass. 1. What is Compass? In simple, Compass it the toolkit of Sass. Sass itself is only a compiler, Compass...

   Compass,CSS,Sass,Tutorial     2012-12-03 13:35:46

  Recover deleted file in Linux EXT3 file system

Environment : CentOS 5.3 x86_64, /dev/sdb1 is the data segment /data0. EXT3 file system. Problem : /data0/tcsql/cankao/phpcws-1.5.0/httpcws.cpp is deleted mistakenly and httpcws.cpp is not backed up. It will take much time to rewrite this program again. So we must recover it back. debugfs is feasible in EXT2 file system, but in EXT3 file system, it's not very useful. There is one open source software called ext3grep which can help us recover deleted file in EXT3 file system. The recovery steps a...

   Linux,EXT3,File recovery     2013-08-16 07:06:45

  Books for entry level C programmers

In computing, C is a general-purpose programming language initially developed by Dennis Ritchie between 1969 and 1973 at Bell Labs Its design provides constructs that map efficiently to typical machine instructions, and therefore it found lasting use in applications that had formerly been coded in assembly language, most notably system software like the Unix computer operating system.To learn C, we need to read many C books and have many practices. Here we summarize a list of C books which may h...

   C,Book,Beginning     2012-07-26 14:00:51

  Google is developing advanced programming technology to simplify Web application development

Beijing, March 28. According to foreign media reports, Google engineer Alex Russell this week at EclipseCon meeting said the company is now developing lots of advanced programming techniques to simplify Web application development.Russell said, "Web development has come to a critical point, it is becoming a run-time library integration platform." Although Web is very popular compared to some platforms such as Java or Windows, it provides only a relatively original programming capability. A ...

   Google,Web,Dart,Scalability     2012-03-30 06:22:13

  Screen recording in Windows 10

Have you ever wondered how to take screen recording easily on Windows? Normally you would think to download some software online and install it on your machine such as Camtasia. However, many of them are either non-free or uneasy to use. Fortunately, there is a built-in tool provided in Windows 10 which can be used to take simple screen recording plus audio recording. The tool is called the Game Bar which is primarily intended for gamers to take screenshots of their plays and achievements. Don't...

   WINDOWS 10,GAME BAR,SCREEN RECORDING     2018-03-06 11:42:07

  The evolving history of asynchronous operation in JavaScript

JavaScript is single threaded, it means there would be only one task running at any point of time. But this would slow down the overall program execution if there is long running task, hence asynchronous task execution is desired in complex cases. To achieve asynchronous task execution, there are a few options introduced in JavaScript. setTimeout/setInterval Event Promise Async/Await setTimeout/setInterval is one of the first mechanisms introduced in JavaScript to simulate asynchronous operati...

   JAVASCRIPT,ASYNC,PROMISE,AWAIT     2019-11-09 08:21:56

  Java 9 release is delayed again

The original Java 9 planned release date is March 2017. But latest source shows that Java 9 release will be delayed again to July 2017. It's four months later than the planned date. Oracle Chief Architect of Java Platform group Mark Reinhold proposes this new release date in a message sent on the OpenJDK mailing list.  Despite this progress, at this point it's clear that Jigsaw needs more time. We recently received critical feedback that motivated a redesign of the module ...

   JAVA,RELEASE DATE,JAVA 9,JAVA 9 DELAY     2016-09-26 12:22:53

  OpenLDAP Proxy -- rwm-map vs map

OpenLDAP proxy is used to proxy ldap request and response between clients and servers, different servers may have different representations/attributes to mean the same thing. For example, in one LDAP server, the firstName may be represented by firstName, it may be represented by givenName in a different server. However, from the client perspective, it only wants to get the firstName, it doesn't care about the backend attributes. In this case, attribute mapping can help provide a virtual view of ...

   MAP,OPENLDAP,OPENLDAP PROXY,LDAP,RWM-MAP     2018-02-02 20:36:02

  Why cannot compare double values directly for equality?

A question in PHP: Get some value from the database and use floatval() to convert it to floatint point value, then compare it with another value which is also converted to floating point value with floatval(). These two values are the same when using var_dump() to output, the two outputs are float(8.87), they are the same. But when comparing them for equality, the result is weird., they are not equal. Why?To analyze this question, we need to start with PHP data types. PHP uses weak types. In PHP...

   PHP,floating, precision,compare,equality     2012-06-27 09:01:36

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