Want to check whether you are ready for an ETL testing interview? Take this free ETL testing online mock test. It has 20 multiple-choice questions in four parts, the same mix interviewers use: ETL concepts, SQL, data warehouse testing and real scenarios. Each answer comes with a short explanation.
How to Take the Mock Test
- Set a timer for 20 minutes, about one minute per question.
- Write your answer (A–D) for each question before opening "Show answer".
- Give yourself 1 point per correct answer, then read the score guide at the end.
Part 1: ETL Concepts (Q1–Q5)
Q1. In ETL, what does the "T" stand for?
- A. Transfer
- B. Transform
- C. Test
- D. Trigger
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Q2. Which document lists each source column, target column and transformation rule?
- A. Business requirement document
- B. Test summary report
- C. Source-to-target mapping document
- D. Defect log
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Q3. In a star schema, the central table that stores measures such as sales amount is the:
- A. Dimension table
- B. Fact table
- C. Staging table
- D. Lookup table
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Q4. Which slowly changing dimension type keeps full history by inserting a new row with effective dates?
- A. Type 0
- B. Type 1
- C. Type 2
- D. Type 3
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Q5. What is the main purpose of a staging area?
- A. Showing reports to users
- B. Holding extracted data temporarily before transformation
- C. Storing application passwords
- D. Replacing the data warehouse
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Part 2: SQL for ETL Testing (Q6–Q10)
Q6. In Oracle, which operator returns rows in the source query that are not in the target query?
- A. UNION
- B. MINUS
- C. INTERSECT
- D. UNION ALL
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Q7. Which query finds duplicate customer_id values?
- A. SELECT customer_id FROM t WHERE COUNT(*) > 1
- B. SELECT customer_id FROM t GROUP BY customer_id HAVING COUNT(*) > 1
- C. SELECT DISTINCT customer_id FROM t
- D. SELECT customer_id FROM t ORDER BY customer_id
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Q8. How do you find fact rows whose customer_key has no match in the customer dimension (orphans)?
- A. INNER JOIN fact to dimension
- B. LEFT JOIN fact to dimension WHERE the dimension key IS NULL
- C. UNION the two tables
- D. COUNT(*) on the fact table
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Q9. COUNT(email) returns 9,500 and COUNT(*) returns 10,000 on the same table. What does this mean?
- A. The table has 500 duplicate rows
- B. 500 rows have a NULL email
- C. The query is wrong
- D. 500 rows were deleted
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Q10. Comparing SUM(order_amount) in source and target is an example of:
- A. Metadata testing
- B. Aggregate (reconciliation) testing
- C. UI testing
- D. Security testing
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Part 3: Data Warehouse and Testing Types (Q11–Q15)
Q11. Checking that target column data types and lengths match the mapping is called:
- A. Metadata testing
- B. Performance testing
- C. Regression testing
- D. Usability testing
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Q12. What does an incremental load test verify?
- A. That the full table is reloaded every time
- B. That only new or changed records since the last run are loaded, without duplicates
- C. That the report loads quickly
- D. That the source is backed up
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Q13. Analysing source data for nulls, distinct values and ranges before testing is called:
- A. Data masking
- B. Data profiling
- C. Data archiving
- D. Data mining
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Q14. Source and target both have 10,000 rows. What can you conclude?
- A. All data is correct
- B. The total count matches, but values and individual records still need checking
- C. The test passed
- D. There are no duplicates
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Q15. Which of these is usually NOT an ETL tester's task?
- A. Validating transformation rules with SQL
- B. Reconciling report totals with the warehouse
- C. Designing the web page layout
- D. Logging data defects
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Part 4: Scenario Questions (Q16–Q20)
Q16. In a one-to-one load, the target has more rows than the source. What is the most likely cause?
- A. The source was backed up
- B. Duplicates from a wrong join or a job that ran twice
- C. The report is cached
- D. Indexes are missing
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Q17. Rule: full_name = first_name + ' ' + last_name. Some target rows show two spaces between names. Likely cause?
- A. The database is slow
- B. Source names have trailing spaces and the ETL does not trim them
- C. The mapping document is missing
- D. The target column is too long
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Q18. A source row has the date 2026-02-30. What should you normally verify?
- A. That it loads as-is
- B. That it is rejected or routed to an error table as the mapping specifies
- C. That the job stops completely
- D. Nothing, dates are not tested
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Q19. The nightly job finished, but the dashboard still shows yesterday's numbers. What do you check first?
- A. Restart the database
- B. The latest load date or batch ID in the target table and the job audit log
- C. Rewrite the SQL
- D. Change the dashboard colours
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Q20. You find 12 missing records after the load. What should the defect report include?
- A. Only the text "data missing"
- B. The failing query, sample record IDs, the load date and expected vs actual results
- C. A screenshot of the dashboard
- D. The developer's name only
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What Your Score Means
| Score | Where you stand | What to do next |
|---|---|---|
| 17–20 | Interview-ready on the basics | Practise timed, harder sets and scenario questions |
| 12–16 | Good base, some gaps | Revise the parts you missed; drill SQL interview queries |
| 0–11 | Still learning | Follow the ETL testing roadmap and start with ETL testing for beginners |
One short test is a snapshot. For real interview practice, the ETL Testing Interview Questions & Answers – Practice Tests on Udemy have 500+ questions with detailed answers, including SQL and scenario-based questions, from fresher to experienced level.
Prepare for your ETL testing interview: top 50 questions · in-depth answers · for experienced (3–5 years) · for 10 years experience · SQL query questions · scenario-based questions · data warehouse questions · questions for freshers · database testing questions
More guides for Indian students: ETL full form · ETL testing with example · ETL testing jobs in India · ETL testing course in India · ETL training in Hyderabad, Bangalore & Pune · best ETL testing course on Udemy · ETL testing roadmap · ETL tester vs ETL developer · interview questions for freshers · SQL for testers · QA to data engineer · ETL testing kya hai (Hindi)
Frequently Asked Questions
Where can I take a free ETL testing online mock test?
This page has a free 20-question ETL testing mock test with answers covering ETL concepts, SQL, data warehouse testing and scenarios. For more practice, Udemy has ETL testing practice tests with 500+ questions.
What topics are in an ETL testing mock test?
A good ETL testing mock test covers ETL concepts, source-to-target mapping, SQL queries for validation, data warehouse concepts such as facts, dimensions and SCDs, testing types, and real scenarios.
How many questions should I practise before an ETL testing interview?
Aim for a few hundred questions across concepts, SQL and scenarios, and write the SQL yourself rather than only reading answers. Timed practice tests help you answer confidently.
Is this mock test good for freshers?
Yes. The questions are fresher to junior level. If you score below 12, revise SQL and data warehouse basics first.
How is an ETL testing mock interview different from a mock test?
A mock test checks knowledge with multiple-choice questions. A mock interview asks you to explain answers, write SQL and walk through a project out loud, so practise both.
Asim Noaman Lodhi
Certified Google Partner · QA Consultant · 12+ Years IT
QA consultant specializing in ETL testing and data quality. Trained 913+ students to transition into data testing roles through hands-on, real-world instruction.