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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 Hadoop is Better for Legacy data

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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