Updated March 2, 2023
Introduction to ETL Testing Interview Questions and Answers
Business information and data are the most important things any business these days. Analyzing all the data and integrate these results has gained a huge potential in the market. There are many ETL testing tools which help in having a process organized and simpler. ETL testing must have a well-defined strategy which makes this entire process easier. The process includes analyzing the requirement, Validation and Test Estimation, Test Planning and Designing the testing environment, Test Data preparation and Execution and creating a Summary Report. The extract, transform and load process needs loads of analysis and as a result, needs proper testing. The following questions will give you an insight all the questions that can be asked in an interview.
Now, if you are looking for a job which is related to ETL Testing then you need to prepare for the 2023 ETL Testing Interview Questions. It is true that every interview is different as per the different job profiles. Here, we have prepared the important ETL Testing Interview Questions and Answers which will help you get success in your interview.
In this 2023 ETL Testing Interview Questions article, we shall present 10 most important and frequently used ETL Testing interview questions. These questions are divided into two parts are as follows:
Part 1 – ETL Testing Interview Questions (Basic)
This first part covers basic ETL Testing Interview Questions and Answers
Q1. What is ETL and explain why ETL testing is required?
Answer:
ETL is an abbreviation for extract, transform and load. This process is done for the data which is used to analyze and predict the future of any business. Extracting means locating the data and removing from the source file all the data. Transforming is the process of transporting the data to any required file and loading this file to the target system in the format which is requested or applicable. The need for ETL testing arises as we need to keep a track on data which is being transformed from one system to another. We also need to check the efficiency and speed of this entire process. ETL testing ensures that all data that is being implemented is as per the requirements of the client and provides the necessary output.
Q2. What is the surrogate key?
Answer:
A surrogate key can be said as a unique identifier which can be used for modeling an entity or an object. It can be a unique key whose significance is to be a primary identifier of any object or entity which is not derived from any other database and cannot be used as a primary key. The surrogate key can be a unique sequential number. A surrogate key is not always a primary key and it usually depends on the database. It chooses if the database is current or of a temporal kind. When a database is current it stores the current data and needs to have a one to one relationship in data. When it comes to the temporal database there can be a many to one relationship between the primary and surrogate keys.
Let us move to the next ETL Testing Interview Questions.
Q3. Explain what is partitioning and explain the types of partitions?
Answer:
In order to improve performance, the transactions present are subdivided and this process is known as partitioning. Partitioning helps Informatica Server to create different connections to its various sources. The types of partitions are:
Round Robin Partitioning: All data is evenly distributed among all partitions. In all these partitions when the number of rows is approximately the same then this partitioning is used.
Hash Partitioning: In this partitioning, all partitioning keys are grouped among the partitions apply a hash function. It is used to ensure the processed group of rows with the same partitioning key have the same partitions.
Q4. What are the ways of updating a table when SSIS is being used?
Answer:
This is the common ETL Testing Interview Questions asked in an interview. Please find below the different tables that are supported by ETL Testing are. To update a table using SSIS the following steps can be performed:
- Use SQL command
- Use a staging table to store stage data
- Use cache to store data which uses limited space and requires frequent refresh
- Use Scripts to schedule tasks
- Make use of full database name for updating MSSQL.
Q5. What is a staging area and what is its purpose?
Answer:
Data staging is usually a collection of processes which is used to prepare the source system data. This data is then loaded into the data warehouse. Data staging includes the following steps:
Source data extraction and data transformation where data is restructured as per customer requirements. Data transformation includes the process of data cleansing and value transformations. It also involves the process of surrogate key assignments.
Part 2 – ETL Testing Interview Questions (Advanced)
Let us now have a look at the advanced ETL Testing Interview Questions.
Q6. Explain the difference between ETL testing and database testing?
Answer:
The difference between ETL testing and database testing is as below:
- ETL testing usually focuses on business intelligence reporting while database testing involves an integration of data.
- The tools that are used for ETL testing are Cognos, QuerySurge, and Informatica while QTP and selenium are used for automation of database testing.
- The analysis of data in ETL has a potential impact on data. The normal database testing has architectural implementation impacts
- ETL testing has deformalized data while database testing uses normalized data.
Q7. What is a fact? Explain the types of facts?
Answer:
A fact is a central component of a multidimensional model which consists of the measures which are to be analyzed. Facts are related to different dimensions.
The types of facts are as below:
Additive: A measure can perform arithmetic calculations by using all or some dimensions.
Semi-additive: In this type, a measure can perform arithmetic calculation by using only some dimensions.
Non-additive: A measure cannot participate in arithmetic functions by using dimension.
Let us move to the next ETL Testing Interview Questions.
Q8. What is the difference between the surrogate key and primary key?
Answer:
A Surrogate key is said to have sequentially generated numbers which have no meaning. It is just used so as to identify the rows present uniquely. Primary key, on the other hand, is used to identify rows uniquely. It is visible to users and it can be changed as per requirements.
Q9. Define the term slow changing dimension.
Answer:
This is the most asked ETL Testing Interview Questions in an interview. Slow changing dimensions are those which tend to change very slowly. The data present in these dimensions are slow to change. Example of this dimension can be a city or an employee.
The rows in these data in the dimensions can be either replaced completely without having any track record or a new row can be created or inserted. By using this the slow changes can also be tracked.
Q10. Explain the concept of data purging?
Answer:
Deleting a piece of data from the data warehouse is known as data purging. This data which is deleted is usually data which has rows with null values or spaces which need clean up. In this process cleaning of this kind of garbage or junk, values are done.
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