Through this blog, we will assist you to move ahead in your ETL testing career. Our motive is to provide an easy career path without any difficulties. It guides you through the basic to advanced level questions. These These Top 40 ETL Testing Interview Questions with answers that employers generally ask during ETL testing job interviews.
ETL stands for extract, transform, and load. These are the three functions of databases that are combined into a single tool. This combination allows you to take out data from a particular database and store or keep it in another.
If you are looking for ETL testing interview questions for freshers or seniors. You are at the right place. There are a lot of opportunities from many reputed companies in the world. According to research, ETL testing has an extended market share. So, you still have the opportunity to move ahead in your career in ETL testing analytics.
Go through the ETL interview questions listed below and make sure to prepare them before going for your job interview. But before we share the questions, let us have a look at what ETL is.
ETL: Extract – Transform – Load
ETL is a data integration process. It refers to the three distinct, interrelated steps of extract, transform, and load. The process involves extracting data from different systems and transforming it. Then load it into appropriate data warehouses.
Using ETL, businesses can gather data from a variety of sources. It can consolidate it into one centralized location. The three functions are defined as follows:
- Extract. This is the process of gathering data from multiple sources.
- Transform. In this step, the data is converted into a form that can be stored in the database. In the transformation process, related data are combined with other data using rules or lookup tables.
- Load. This is the process of writing the data into the correct database.
Anyone with experience in data hubs, data warehouses, or data lakes will understand the need to extract, transform, and load data. It is an excellent approach to data processing that will result in better performance.
Top 40 ETL Testing Interview Questions With Answers
1. What Is ETL Testing?
ETL testing is done to ensure that the data is loaded from different sources to destinations. We load data to the destination after the accurate business transformation. It involves data verification at multiple stages that we use between the source and the destination.
2. What Is An ETL Process?
In data processing, data has to be transferred from one database to another. This process is known as the ETL process. The ETL process includes extraction (E), transformation (T), and loading (L) processes. In the extraction process, the data is extracted from a source. It is then worked on during the transformation phase. The data is transformed into a standard format suitable for the new target data warehouse. At last, in the loading phase, transformed data is loaded into the destination database.
3. What Are The Steps Of An ETL Testing Process?
Although there are many ETL tools, there is a simple testing process commonly used in ETL testing. It is as important as the implementation of the ETL tool in your business. Having a well-defined ETL testing strategy can make the testing process much easier. Hence, this process needs to be completed before you start the data integration with the selected ETL tool.
In this ETL testing process. A group of experts comprising the programming and developing team will start writing SQL statements. The development team may customize them according to the requirements.
ETL testing process has the following stages:
- Analyzing Requirements. Understanding the business structure and its particular requirements.
- Validation And Test Estimation. Estimating the time and expertise required to carry on with the procedure.
- Test Planning And Designing The Testing Environment. Based on the inputs from the estimation is planned and worked out.
- Test Data Preparation And Execution. Data for the test is prepared and executed as per the requirements.
- Summary Report: Upon the completion of the test run, a summary report is prepared for improvising and concluding.
4. What Is The Use Of ETL?
ETL is used to seamlessly migrate data from one database to another. The process is efficient when loading data from data warehouses and data marts. It is also reliable in converting the format of large databases.
In the digital era, most businesses recognize the need to prepare data and store it properly. The use of ETL has made it a go-to solution for many companies and corporations. Below are some of the possible uses of ETL:
Providing Historical Context
Businesses can acquire historical context when using ETL with an enterprise data warehouse. It provides extended reference material for both old and new data.
Giving A Consolidated View
ETL provides a common data repository. This makes it easier to analyze, visualize, and evaluate large data sets.
With ETL, there is no need for technical assistance, as it can code and reuse processes to transfer data. There is no need to hand-code a migration of big data.
Making Business Decisions
Companies can make well-informed decisions. When they are strategizing based on proper data analysis. ETL can be used to tackle complex business problems. These are the problems that a traditional database could not handle.
5. What Are The Responsibilities Of ETL Testers?
Responsibilities Of ETL testers include:
- The tester requires in-depth knowledge of the ETL tools and processes.
- An ETL tester needs to carry out quality checks on a regular basis.
- ETL tester tests the ETL software thoroughly.
- The tester will check the test components of the ETL data warehouse.
- The tester will execute the data-driven test in the backend.
- The tester creates the design and executes the test cases, test plans or test harness, etc.
- The tester identifies the problems and will suggest the best solution also.
- The tester approves the requirements and design specifications.
- Tester transfers the data from flat files.
- They write the SQL queries for the different test scenarios.
6. Can There Be Sub-Steps For Each Of The ETL Steps?
Each of the steps involved in ETL has several sub-steps. The transform step has more sub-steps.
7. Explain The ETL Testing Operations?
The ETL testing involves the below-mentioned operations:
- It will validate the data movement from the source to the target system.
- It does the data count verification in the source and target system.
- It verifies the transformation and extraction as per requirements and expectations.
- It verifies if table relations join and keys are preserved during transformation.
8. What Is The Three-Layer Architecture Of An ETL Cycle?
The three layers in the ETL are:
The staging layer is used to store the data which is extracted from the different data source systems.
Data Integration Layer:
The integration layer transforms the data from the staging layer and moves the data to a database. In the database, the data is arranged into hierarchical groups. It is often called dimension. The data is also arranged into facts and aggregation facts. The combination of facts and dimension tables in a data warehouse system is called a schema.
The access layer is used by the end-users to retrieve the data for analytical reporting.
17. What Are The ETL Tools Available In The Market?
The popular ETL tools available in the market are:
- IBM- Websphere DataStage
- Informatica- Power Center
- SAP- Business objects data service BODS
- SAS – Data Integration Studio
- Oracle- Warehouse Builder
- Open source Clover ETL.
18. What Is A Data Mart?
Data Mart is a simple form of Data Warehouse. It is focused on a single functional area. It comes only from a few sources.
For Example. In an organization, data marts may exist for marketing, finance, HR, and other individual departments. These departments store the data related to their specific functions.
19. What Are Initial Load And Full Load?
The initial load is the process of populating all data warehousing tables for the first time. In full load, when the data is loaded for the first time. All set records are loaded at a stretch depending on their volume. It would erase all contents from the table and would reload the fresh data.
20. What Is The Need For ETL Testing?
In today’s time, we are migrating lots of systems from old technology to new technology. At the time of migration activities, we also need to migrate the data as well from the old DBMS to the latest DBMS. So there is a lot of need to test whether the data is correct from the target side.
Here, are some important points where the need for ETL testing is arising:
- ETL testing is used to keep an eye on the data which is being transferred from one system to another.
- The need for ETL testing is to keep track of the efficiency and speed of the process.
- The need for ETL testing is arising to be familiar with the ETL process before we implement it into our business and production.
21. How Do We Use ETL In Third-Party Management?
The big organization always gives different application development to different kinds of vendors. A single vendor cannot manage everything. Here we are taking an example of a telecommunication project.
In telecommunication, billing is handled by one company, and another company manages CRM. If a CRM company needs the data from the company, that is managing the billing. Now the company will receive the data feed from another company. To load the data from the ETL process is used.
22. What Are Cubes And OLAP Cubes?
Cubes are data processing units composed of fact tables and dimensions from the data warehouse. They provide a multi-dimensional analysis.
OLAP stands for ‘Online Analytics Processing,’ and OLAP Cubes store voluminous data in a multi-dimensional form for reporting purposes. They consist of facts called ‘measures’ categorized by dimensions.
23. What Is Workflow In ETL?
Workflow is a set of instructions that specify the way of executing the tasks to the Informatica.
24. What Is The Benefit Of Increasing The Number Of Partitions In ETL?
An increase in the number of partitions enables the Informatica server to create multiple connections to a host of sources.
25. What Are The Types Of Partitions In ETL?
Types of partitions in ETL are the Round-Robin partition and Hash partition.
26. What Is Mapping In ETL?
Mapping refers to the flow of data from the source to the destination.
27. What Is A Session In ETL?
A session is a set of instructions that describe the data movement from the source to the destination.
28. What Is Meant By Worklet In ETL?
Worklet is a set of tasks in ETL. It can be any set of tasks in the program.
29. How Do We Use ETL In Data Warehousing?
Most commonly, the ETL is used in Data Warehousing. The user fetches the historical data as well as current data for developing the data warehouse.
Data in the data warehouse is the combination of historical data as well as transactional data. Data sources of data warehouses might be different. We need to fetch the data from multiple different systems. We then load it into a single target system, which is also called a data warehouse.
30. What Is Meant By Incremental Load?
Incremental load refers to applying dynamic changes as and when required in a specific period and predefined schedules.
31. List The Types Of Data Warehouse Applications?
- Info Processing
- Analytical Processing
- Data Mining
32. What Is Round-Robin Partitioning?
In Round-Robin partitioning, the data is evenly distributed by Informatica among all partitions. It is used when the number of rows in the process in each of the partitions is nearly the same.
33. What Is Hash Partitioning?
In Hash partitioning, the Informatica server would apply a hash function. It helps the partition keys to group data among the partitions. It is used to ensure the processing of a group of rows with the same partitioning key in the same partition.
34. What Is The Need For A Data Check As A Test Case?
With a data check test case, we can easily get the information that is related to:
- Data check
- Number check
- Null check
35. What Is The Importance Of The Correctness Issue Test Case?
The correctness issues test case will help us in understanding the following:
- Misspelled data
- Null data
- Inaccurate data
36. Define Data Source View?
A data source view usually consists of the metadata. It defines the selected objects from one or multiple underlying data sources. Also from the metadata that is used to generate the underlying relational data store.
37. What Do You Know About The Tracing Level And The Types Of The Same?
There are file logs and there is a limit on them when it comes to storing data in them. The Tracing level is nothing but the amount of data that can be easily stored on the same. These levels clearly explain the tracing levels. They explain in a manner that provides all the necessary information regarding the same. There are two types of the same and they are:
38. Do You Have Any Information Regarding The Grain Of Fact?
The fact information can be stored at a level that is known as grain fact. The other name for this is Fact Granularity. The users can change their name when the need for the same is realized. Multiple files are associated with the same. The users can use this for changing the name of all of them directly.
39. It Is Possible To Load The Data And Use It As A Source?
Yes, in ETL it is possible. This task can be accomplished simply by using the Cache. The users must make sure that the Cache is free. They must ensure that it is generally optimized before it is used for this task. At the same time, the users ensure that the desired outcomes can be assured without making a lot of effort.
40. What Is A Factless Fact Table In ETL?
It is defined as the table without measures in the ETL. Many events can be managed directly with the same. It can also record events that are related to the employees or with the management. This task can be accomplished in a very reliable manner.
Bonus ETL Testing Interview Questions
When preparing for an interview, no limit of questions is enough for you to prepare well. This is why we are here to share some bonus questions that might help you with the interview.
1. What Exactly Do You Mean By The Transformation? What Are The Types Of Same?
It is regarded as the repository object which is capable of producing the data. It can even modify and pass it in a reliable manner. The two commonly used transformations are Active and Passive.
2. What Is The Exact Purpose Of An ETL According To You?
It is very beneficial for the extraction of data from the systems that are based on legacy.
3. Can You Define Measure In A Simple Statement?
Well. they can be called the number data which is based on the columns. It is present in a fact table by default.
4. Can You Tell Me Something About Bus Schema?
Dimension identification is very important in the ETL. It is largely handled by Bus Schema.
5. What Do You Mean By Staging Area?
It is an area that is used when it comes to holding the information or the data temporarily. The information or data is held on the server that controls the data warehouse. There are certain steps that are included. The prime one among them is Surrogate assignments.
Some Common Interview Questions About Yourself
To know you better, employers ask these common questions during interviews. These questions hold a chance for you to prove yourself the best fit for the organization. Through these questions, you set your first impression on the employers, which is very important.
Why Did You Choose This Career?
Tell Me Something About Our Company?
Why Should We Hire You?
What Are Your Strengths And Weaknesses?
How You Can Become An ETL Tester – Taking The Best ETL Testing Training Can Help
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ETL Testing Training
ETL testing training certification introduces you to two approaches to converting raw data into analytical data. First is the ETL (Extract, Transform, Load) process. Second is the ELT (Extract, Load, Transform) process. We apply ETL processes to data warehouses and data marts. We apply ELT processes to data lakes. It is where we transform data on demand by requesting or calling applications.
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