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SQL Interview Success: Unlocking the Top 5 Frequently Asked Queries

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 Here are the five top commonly asked SQL queries in the interviews. These you can expect in Data Analyst, or, Data Engineer interviews. Top SQL Queries for Interviews 01. Joins The commonly asked question pertains to providing two tables, determining the number of rows that will return on various join types, and the resultant. Table1 -------- id ---- 1 1 2 3 Table2 -------- id ---- 1 3 1 NULL Output ------- Inner join --------------- 5 rows will return The result will be: =============== 1  1 1   1 1   1 1    1 3    3 02. Substring and Concat Here, we need to write an SQL query to make the upper case of the first letter and the small case of the remaining letter. Table1 ------ ename ===== raJu venKat kRIshna Solution: ========== SELECT CONCAT(UPPER(SUBSTRING(name, 1, 1)), LOWER(SUBSTRING(name, 2))) AS capitalized_name FROM Table1; 03. Case statement SQL Query ========= SELECT Code1, Code2,      CASE         WHEN Code1 = 'A' AND Code2 = 'AA' THEN "A" | "A

AWS EMR Vs. Hadoop: 5 Top Differences

With Amazon Elastic MapReduce Amazon EMR, you can analyze and process vast amounts of data. It distributes the computational work across a cluster of virtual servers ( run in the Amazon cloud). An open-source framework of Hadoop manages it. 



AWS EMR Vs. Hadoop




Amazon EMR - Elastic MapReduce, The Unique Features


  • Amazon EMR has made enhancements to Hadoop and other open-source applications to work seamlessly with AWS.
  • For instance, Hadoop clusters running on Amazon EMR use EC2 instances as virtual Linux servers for the master and slave nodes, Amazon S3 for bulk storage of input and output data, and CloudWatch to monitor cluster performance and raise alarms.
  • Also, you can move data into and out of DynamoDB using Amazon EMR and Hive. That orchestrates by Amazon EMR control software that launches and manages the Hadoop cluster. This process is called an Amazon EMR cluster.


What does Hadoop do?


Hadoop uses a distributed processing architecture called MapReduce, in which a task maps to a set of servers for processing.


  • The results of the computation performed by those servers reduce to a single output set.
  • One node, designated as the master node, controls the distribution of tasks. The following diagram shows a Hadoop cluster with the master node directing a group of slave nodes which process the data.
  • One Master node handles multiple slave nodes. All open-source projects run on the Hadoop architecture can also be run on Amazon EMR. The most popular applications, such as Hive, Pig, HBase, DistCp, and Ganglia, are already integrated with Amazon EMR.


By running Hadoop on the Amazon EMR, you will get the following benefits of the cloud:


  1. The ability to provision clusters of virtual servers within minutes.
  2. You can scale the number of virtual servers in your cluster to manage your computation needs and only pay for what you use. 
  3. Integration with other AWS services.

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