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ETL Interview Questions with answers

A wide array of ETL interview questions from basic to advanced level to help you ace the interview of your dream profile.

ETL or Extract Transform Load testing has revolutionized the way data analysis and integration have been perceived. It has tapped a vast potential market for those well versed in it, therefore commencing the hiring haul across various companies. Various free Softwares can be exploited, but the problem is they are less sophisticated. Companies, owing to their different structures and business models, can’t rely on them. Therefore, they mostly avail ETL subscription plans. This growing flow of ETL testing services requires skillful labor that can make use of it. So, companies are always keeping an eye for such intelligent beings, and the selection process has to go through an ETL testing interview.

Answering all the testing interview questions requires practice and a basic pattern thereof, which is provided below.

Basic ETL interview questions 

Every profile in a company asks for basic interview question answers at the time of its commencement. So is the case here.

1. What do you understand about an ETL process?

ETL process consists of data Extraction, Transformation, and Loading from any outside system to the required setting. Data integration process is followed in these 3 stages, where extraction refers to identifying the data and removing it from its original file, transforming involves carrying it to the desired file and then loading this file to the target system in the most efficient way.

2. What is the need of ETL testing?

ETL testing is needed for:

  • To act as a checker on the bulk of data while it is being transferred from one system to another.
  • Tracking the overall efficiency and speed of the process.
  • To get familiarized with the working of ETL process, so that it can be later implemented into business structures without any impediment.

3. ETL tester has to undertake what kind of responsibilities?

  • He has to be well versed in the ETL tools and processes.
  • Needs to know how to write SQL queries for various situations during the phase of testing.
  • Quality checks need to be transacted regularly.

4. Name some tools that are used in ETL

  • SAS business Warehouse
  • SAS Enterprise ETL server
  • Oracle Warehouse Builder
  • Cognos decision stream
  • Business Object XI

5. What is the Tri-layered architecture of an ETL cycle?

  • Staging Layer: it is used to store the data that is extracted from other varied data source systems.
  • Data integration layer: After transforming the data from the staging layer, it moves the data to a particular database.
  • Access Layer: In order to carry out analytical reporting, the access layer is used by end-users.

6. When do we require a staging area in the ETL process?

Between the data sources and the data warehouse systems, a central area called a staging area lies. The data integration process is the place where data is stored temporarily. In the staging, area data is checked upon for cleansing and therefore preventing it from any duplication. It helps in increasing efficiency, ensuring data integration. And wielding various qualitative data operations.

7. Distinguish between data warehouse and data mining?

The concept of a data warehouse is relatively vast. Data warehousing involves consolidating data from various sources while keeping the data quality, consistency, and accuracy intact. It is used for supporting managerial tasks. At the same time, data mining encodes and identifies data patterns from a more comprehensive set of data. It helps in making the company aware of the general mood and activities of the consumers. It can also deter any activity with fraudulent intent.

Intermediate ETL interview questions

Now we have come to the second stage of the testing interview questions that will prove your further mettle in the field. 

8. Can you define ETL processing?

Simple testing is the prelude to any further data integration activity in the data management process. There is one simple testing process that is widely used in ETL testing. A well-structured ETL strategy can prove to be effective

ETL testing process follows these stages:

  • Carefully examining and analyzing requirements: Different companies have different business structures, implying that their conditions also differ. Therefore, a thorough understanding needs to be developed.
  • Test estimation: Estimating the total time and skills that would be deployed in carrying on with the procedure
  • Planning of ETL environment: based on the results from the estimation, a proper ETL environment is charted out.
  • Preparation and Execution:  systematic preparation and execution of data for the test, depending upon the requirements
  •  Upshot Report: After having completed the testing. A brief summary is produced for the purpose of any improvisation and refinement.

9. What do ETL testing operations consist of?

  • Verification of whether the data is accurately transformed to suit the requirements of businesses
  • Verification of whether the integrated data has loaded into the data warehouse without any hindrance, in the form of any sort of data loss.

10. Give a list of a few ETL bugs.

  • Source bug
  • Calculation bug
  • User interface bug
  • Load condition bug
  • ECP related bug

11. What do you understand by a fact? What is its type?

A fact is a numeric value that the business wishes to consider and contains the measures to be analyzed.

Types of facts include:

  • Additive fact
  • Non-additive facts
  • Semi additive facts

12. What do you understand from snapshots?

Snapshots refer to a read only data that lies in a master table and is a total visualization of data that occurs at the time of its extraction.

13. Define views  

A view can be defined as a logical representation of a table and is built using qualities of one or two of them. It is devoid of any storage of its own and can serve the same purpose as a table.

14. What is a materialized view?

A materialized view refers to an aggregate table that wields the result of a query.

15. State the difference between power center and power mart.

The power center is laden with various options, including distributed metadata, organizing data repositories into a data mart domain, and processing bulk data without much effort. At the same time, the power mart indulges in small-scale data processing, which lacks features of the power center.

16. What do you understand by data purging and how is it different from deletion?

The process of removing and erasing data from the data space is known as data purging. Deletion may not be able to fulfill this task permanently; that’s where data purging comes into the picture; it always removes the data, and as a result, a lot of storage space is made, which can later be utilized for other uses.

17. How would one differentiate between ETL tools and OLAP tools?

ETL is the extraction and transformation of data and loading it into a specific database with the help of various tools for a particular purpose.OLAP tools, on the other hand, also extract data but through simple queries. 

Advanced ETL interview questions

This stage of the ETL interview would require the fullest of your knowledge in testing and therefore nudge you more complex than any of the steps you faced before.

18. What is the overall usefulness of increasing the number of partitions in ETL?

The more the number of partitions the more it is beneficial for enabling the informatica server to produce multiple connections with a host server.

19. What is round robin partitioning?

Round-robin partitioning is used to achieve equal distribution of rows and data by Informatica to the created partitions.

20. What is hash partitioning?

Within the database, the process of separating rows and evenly spreading them out in sub-tables ensures that the group of rows lies with the same partitioning key in the same partition.

21. Define session in an ETL.

Session is a group of instructions that manipulate the data from its source to the target specified. It can be either executed sequentially or concurrently.

22. What is an operational data store?

Between the staging area and the data warehouse there exists a repository called an operational data store. Stored data lying in ODS has low granularity.

23. How does the ODS or operational data store work?

Before the aggregated data is populated in the ODS, it is loaded in the EDW or Enterprise Data Warehouse. Thus, it majorly helps in analyzing the business data.

24. What does the ODS in ETL generate?

ODS in ETL generates primary keys, prevents errors and exudes DWH like rejecting practices. 

Conclusion

Preparing all of the above ETL interview questions would not be sufficient, as mentioned earlier you must have complete knowledge of the technicality and application of testing. However, these ETL question answers follow from a basic pattern that has become a recurring theme in all ETL interviews.

1. Is an ETL testing interview difficult to crack?

The answer totally depends upon the kind of preparation that you have, the more ETL question answers you have prepared the better the chances of success.

2. How long does an ETL interview last?

It varies from company to company. In most cases they tend to ask questions besides the technical ones therefore taking the time duration to more than 1 hour but the bottom line is that it is not certain.

3.What are the important ETL interview questions?

The questions mentioned above are deemed necessary from the experience of various candidates who have sat in an ETL interview. So, you might want to prepare them.

4. What is the scope of ETL testing in India?

With an upsurge in the number of companies in India, the demand for ETL testers have increased significantly and will continue to be so for the time being.

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