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ETL Testing – Interview Questions

  • What do you understand by an ETL?
  • Explain the 3-layer architecture of an ETL cycle.
  • What is the difference between and ETL and BI tools?
  • What are the popular ETL tools available in the market?
  • Why do we need a staging area in an ETL process?
  • What is the difference between data warehousing and data mining?
  • What are the structural differences between an OLTP and OLAP system?
  • What is a Dimension table and how is it different from a Fact table?
  • What is a Data Mart?
  • What is an Aggregate function?
  • Name a few common aggregate functions.
  • Explain the difference between DDL, DML, and DCL statements.
  • What is an Operator in SQL?
  • Explain common operator types.
  • What are the common set operators in SQL?
  • What is the difference between Minus and Intersect?
  • What is their use in ETL testing?
  • Explain ‘Group-by’ and ‘Having’ clause with an example.
  • What do you understand by ETL Testing?
  • How ETL Testing is different from database testing?
  • What are the different ETL Testing categories as per their function?
  • Explain the key challenges that you face while performing ETL Testing.
  • What are your responsibilities as an ETL Tester?
  • What do you understand by the term ‘transformation’?
  • What do you understand by Active and Passive Transformations?
  • What is Partitioning?
  • Explain different types of partitioning.
  • What is the difference between round-robin partitioning and Hash partitioning?
  • Explain the terms − mapplet, session, mapping, workflow − in an ETL process?
  • What is lookup transformation and when is it used?
  • What is a surrogate key in a database
  • ?What is the difference between surrogate key and primary key?
  • If there are thousands of records in the source system, how do you ensure that all the records are loaded to the target in a timely manner?
  • What do you understand by Threshold value validation Testing?
  • Explain with an example.
  • Write an SQL statement to perform Duplicate Data check Testing.
  • How does duplicate data appear in a target system?
  • What is Regression testing?
  • Name the three approaches that can be followed for system integration.
  • What are the common ETL Testing scenarios?
  • What is data purging?
  • What do you understand by a cosmetic bug in ETL testing?
  • What do you call the testing bug that comes while performing threshold validation testing?
  • I have 50 records in my source system but I want to load only 5 records to the target for each run.
  • How can I achieve this?
  • Name a few checks that can be performed to achieve ETL Testing Data accuracy.
  • Which SQL statements can be used to perform Data completeness validation?
  • What is the difference between shortcut and reusable transformation?
  • What is Self-Join?
  • What do you understand by Normalization?
  • What do you understand by fact-less fact table?
  • What is a slowly changing dimension and what are its types?

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