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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
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How Hadoop is Better for Legacy data

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Here is an interview question on legacy data. You all know that a lot of data is available on legacy systems. You can use Hadoop to process the data for useful insights.


How Hadoop is Better for Legacy data


1. How should we be thinking about migrating data from legacy systems?


Treat legacy data as you would any other complex data type. 


HDFS acts as an active archive, enabling you to cost-effectively store data in any form for as long as you like and access it when you wish to explore the data.


And with the latest generation of data wrangling and ETL tools, you can transform, enrich, and blend that legacy data with other, newer data types to gain a unique perspective on what’s happening across your business.


2. What are your thoughts on getting combined insights from the existing data warehouse and Hadoop?


Typically one of the starter use cases for moving relational data off a warehouse and into Hadoop is active archiving. 


This is the opportunity to take data that might have otherwise gone to the archive and keep it available for historical analysis.


The clear benefit is being able to analyze data for the types of extended time periods that would not otherwise be cost feasible (or possible) in traditional data warehouses. 


An example would be looking at sales, not just in the current economic cycle, but going back 3 – 5 years or more across multiple economic cycles.


You should look at Hadoop as a platform for data transformation and discovery, compute-intensive tasks that aren’t a fit for a warehouse. 

Then consider feeding some of the new data and insights back into the data warehouse to increase its value.


3. What’s the value of putting Hadoop in the Cloud?

The cloud presents a number of opportunities for Hadoop users. 


Time to benefit through quicker deployment and eliminating the need to maintain cluster infrastructure Good environment for running proofs-of-concept and experimenting with Hadoop.


Most Internet of Things data is cloud data.


Running Hadoop in the cloud enables you to minimize the movement of that data The elasticity of the cloud enables you to rapidly scale your cluster to address new use cases or add more storage and compute.

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