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SQL Query: 3 Methods for Calculating Cumulative SUM

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SQL provides various constructs for calculating cumulative sums, offering flexibility and efficiency in data analysis. In this article, we explore three distinct SQL queries that facilitate the computation of cumulative sums. Each query leverages different SQL constructs to achieve the desired outcome, catering to diverse analytical needs and preferences. Using Window Functions (e.g., PostgreSQL, SQL Server, Oracle) SELECT id, value, SUM(value) OVER (ORDER BY id) AS cumulative_sum  FROM your_table; This query uses the SUM() window function with the OVER clause to calculate the cumulative sum of the value column ordered by the id column. Using Subqueries (e.g., MySQL, SQLite): SELECT t1.id, t1.value, SUM(t2.value) AS cumulative_sum FROM your_table t1 JOIN your_table t2 ON t1.id >= t2.id GROUP BY t1.id, t1.value ORDER BY t1.id; This query uses a self-join to calculate the cumulative sum. It joins the table with itself, matching rows where the id in the first table is greater than or

How to Setup Hadoop Cluster Top Ideas

Hadoop cluster setup in Centos Operating System explained in this post. So you can install CentOs either in your Laptop or in Virtual Machine.
Hadoop cluster setup proces
Hadoop Cluster Setup Process

9 Steps Process to Setup Hadoop Cluster

Step 1:  Installing Sun Java on Linux. Commands to execute for the same:
sudo apt-add-repository ppa:flexiondotorg/java
sudo apt-get update
sudo apt-get install sun-java6-jre sun-java6-plugin
sudo update-java-alternatives -s java-6-sun

Step 2:  Create Hadoop User. Commands to execute for the same:
$sudo addgroup hadoop
$sudo adduser —ingroup hadoop hduser

Step 3:  Install SSH Server if not already present. Commands are:
$ sudo apt-get install openssh-server
$ su - hduser
$ ssh-keygen -t rsa -P ""
$ cat $HOME/.ssh/id_rsa.pub >> $HOME/.ssh/authorized_keys

Step 4:  Installing Hadoop. Commands for the same are:
$wget http://www.eng.lsu.edu/mirrors/apache/hadoop/core/hadoop-0.22.0/hadoop-0.22.0.tar.gz
$ cd /home/hduser
$ tar xzf hadoop-0.22.2.tar.gz
$ mv hadoop-0.22.2 hadoop

Step 5:  Edit .bashrc. Commands:
# Set Hadoop-related environment variables
export HADOOP_HOME=/home/hduser/hadoop
# Set JAVA_HOME (we will also configure JAVA_HOME directly for Hadoop later on)
export JAVA_HOME=/usr/lib/jvm/java-6-sun

Step 6:  Update hadoop-env.sh
Here we need to only update the JAVA_HOME variable, we just need to open the file from text editor.
$vi /home/hduser/hadoop/conf/hadoop-env.sh
And update the following:
export JAVA_HOME=/usr/lib/jvm/java-6-sun

Step 7:  Update the files residing in the conf folder.  The three main files are:
Core-site.xml
Mapred-site.xml
Hdfs-site.xml
Here we need to change the value of namenode and jobtracker to where we want to run.

Step 8:  Start the hadoop cluster, using command.
Start-all.sh

Step 9:  Check if all the processes are up and running, using command:
Jps
That’s it. The cluster should be up and running with the following 5 processes:
  • NameNode
  • SecondaryNameNode
  • DataNode
  • JobTracker
  • TaskTracker
If we see all these processes, it means our installation is successful and the cluster is up and running.

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