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  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

  Generate certificate with cRLDistributionPoints extension using OpenSSL

In an X509 certificate, the cRLDistributionPoints extension provides a mechanism for the certificate validator to retrieve a CRL(Certificate Revocation List) which can be used to verify whether the given certificate is revoked.   A cRLDistributionPoints extension can contain one or more DistributionPoints where the CRL can be retrieved from. Each DistributionPoint consists of three fields,each of which is optional: distributionPoint : it contains either a SEQUENCE of general...

   X509,OPENSSL,CERTIFICATE,CRLDISTRIBUTIONPOINT,EXTENSION     2015-10-22 03:41:11

  Launch Java process programmatically in Java

In some cases while working on some automation testcase, developers would like to launch Java process programmatically so that the tests can be ran without manual intervention. Java provides such methods to achieve this. ProcessBuilder can be used to build a Java process which can be launched when everything is ready. Basically it can take a list of parameters which are similar to the command line options/arguments.  For example, if you want to launch a Java process, you can do followi...

   JAVA,PROCESSBUILDER,COMMAND LINE     2016-04-27 04:03:30

  Different types of keystore in Java -- Windows-MY

Windows-MY is a type of keystore on Windows which is managed by the Windows operating system. It stores the user keys and certificates which can be used to perform cryptographic operations such as signature verification, data encryption etc. Since it's a kind of native keystore, Java doesn't have a general API to access it. To help Java applications access the keys and certificates stored in Windows-MY keystore, Java provides a separate API -- SunMSCAPI. The SunMSCAPI provider is ...

   JAVA,KEYSTORE,WINDOWS-MY,SUNMSCAPI     2016-01-09 05:45:59

  Server monitoring shell scripts

There are many open source server monitoring software such as cacti and nagios. Besides these, can we write our own shell scripts to monitor them? The shell scripts written by ourselves can fulfill our special requirements better and have a more detailed coverage. Below are some commonly used shell scripts used by Evangelist, an Oracle DBA. 1. Check network gateway traffic #!/bin/bash #network #Mike.Xu while : ; do time='date +%m"-"%d" "%k":"%M' day='date +%m"-"%d' rx_before='...

   Server monitor,CPU,memory,shell     2013-08-30 21:56:14

  A few things Steve Jobs hates doing but his successor did

After Apple released a few "amazing/great" products on 9th September, there are tons of discussions about these new products. The impression most people have is that Apple is losing its capability of innovation and doing things that are NOT different anymore. People will bring back the good memories of Apple when Steve Jobs was still alive everytime when they feel disappointed about the new products Apple released. In this event, Apple released some products which Steve Jobs was hating including...

   Apple,Steve Jobs,Tim Cook,Stylus,Hate     2015-09-11 08:47:13

  Use downcase! with caution in Ruby

Ruby provides ! to change state of some object in place. Hence if you see some functions have ! appended, it means the state of the caller of the function is expected to be changed. This is a very interesting Ruby feature. But sometimes one should be cautious when using this kind of functions because you would get unexpected behavior if using improperly. Let's take an example of String#downcase!. According to the documentation. Downcases the contents of str, returning nil if...

   RUBY,EXCLAMATION MARK,DOWNCASE     2017-02-10 06:34:44

  Java Cipher encryption/decryption example

In Java, Cipher is the API for doing data encryption/decryption. Many cryptographic algorithms such as AES, DES, RC4 etc can be specified when creating Cipher instance. The Cipher instance calls the underlying algorithm specific implementation to do the actual encryption/decryption.  Before doing the encryption/decryption, a key needs to be created and it will be used to do the encryption/decryption. A sample program for performing all these is : import java.security.Key; import javax.cryp...

   Java, Java Security, Cipher, Example, Sample     2015-08-14 07:07:10

  Why do so many technical recruiters suck?

It’s Tuesday, I get a call from an unknown number.  There is a little hesitation, but I finally pick it up.  My number is listed on my business card and I feel like I should get these calls unless I am in a meeting.- Hi, is this Mike?- Yes, speaking….- Hi Mike!  How are you today?- Fine…- I am calling from XYZ Co, and we deal with recruiting and staff augmentation.  I was wondering if you are looking for software developers.We are in San Francisco and itââ...

   Recruitment,HR,Sucks,Tech recruiter     2011-11-13 08:22:02

  The confusing strtotime() function in PHP

Frequently PHP programmers get confused of the use of i month, -1 month, next month in strtotime() function. and hence it leaves some impression to programmer that this function is not that reliable. Let's take one example of strtotime call with -1 month and see why it leaves this impression. date("Y-m-d",strtotime("-1 month"))  // Assume today is 2018-07-31 What's the output of above call? The answer is 2018-07-01. Why not 2018-06-30? So people get confused. It appears that this is ...

   PHP,STRTOTIME,FIRST DAY OF,-1 MONTH     2018-08-04 05:49:32

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