This document discusses interview questions related to ETL testing for business intelligence projects. It begins with questions about challenges in BI testing, what BI and data warehousing are, and key concepts like the data flow in a data warehouse. It then provides examples of different types of testing done on a data warehouse, including attribute checks, duplicate checks, original key checks, and reconciliation checks using sample SQL queries. Finally, it discusses tools that a QA team may use for ETL testing.

1. ETL Testing Interview Questions
• 1. Challenges in the BI Testing field in your previous project.
• 2. What is BI?
The five key stages of Business Intelligence:
1. Data Sourcing
2. Data Analysis
3. Situation Awareness
4. Risk Assessment
5. Decision Support
• 3. What is a Data Warehouse?
The important characteristics of a Data Warehouse:
1. Subject Oriented
2. Integrated
3. Time-variant
4. Non-volatile
• 4. Generally how does the data flow in a Data Warehouse?

2. ETL Testing Interview Questions
• 5. What is a Data Mart?
• 6. What is ETL?
• 7. BI/DW Testing
• 8. What is the need to test a Data Warehouse?
• 9. Data Warehouse Testing and Database Testing
• 10. Type of testing done in a Data Warehouse project
• 11. Who all are involved in testing a data warehouse?
• 12. What are the phases undergone by the QA team?
• 13. How does the QA team prepare test cases?
• 14. Query Format
• 15. OLTP
• 16. OLAP
• 17. Data mining.
• 18. Should we use OLTP design for DWH
• 19. Lookup tables

3. ETL Testing Interview Questions
• 20. Real time DWH
• 21. CDC
• 22. MDM
• 23. What are the tools that a QA team may use?
1. Data access tools (e.g., TOAD, WinSQL) are used to
analyze content of tables and to analyze results of
loads.
2. ETL Tools (e.g. Informatica, Datastage).
3. Test management tool (e.g. Test Director, Quality
Center) that maintains and tracks the
requirements, test cases, defects and traceability
matrix..

4. ETL Testing Interview Questions
• 20. Real time DWH
• 21. CDC
• 22. MDM
• 23. What are the tools that a QA team may use?
1. Data access tools (e.g., TOAD, WinSQL) are used to
analyze content of tables and to analyze results of
loads.
2. ETL Tools (e.g. Informatica, Datastage).
3. Test management tool (e.g. Test Director, Quality
Center) that maintains and tracks the
requirements, test cases, defects and traceability
matrix..

5. ETL Testing Interview Questions
Query format:
Attribute check
Select count(1)
From( Select source table attributes
From source table
Where list of conditions
Except
Select corresponding target table attributes
From target table
Where list of conditions
)alias(alternate name)
Expected output: Count=0
In the above query, we are first retrieving all the attributes from source table which are mapped
to target and then removing from this list all the attributes that are present in target table. So the
result count should be zero, meaning that all the attributes that are present in source table are
present in target table and the test case can be passed.

6. ETL Testing Interview Questions
Query format:
Duplicate Check
Select count(1)
From( Select attribute_list_1
From table_1
Where list of conditions
Group by attribute_list_1
Having count(1)>1
)alias
Expected output: Count=0
In the above query, we are retrieving the attributes which are supposed to be unique and then
grouping them in the same order in which they were retrieved. This will group all the records
which have these attributes duplicated and so the count will be greater than 1 for such records.
When we take the count of such duplicate records and we get zero output, then this shows that
there are no duplicate values for unique columns and the test case can be passed.

7. ETL Testing Interview Questions
Query format:
Original Key Check
Select count(1)
From table
Where list of conditions
And (any of NOT NULL values are NULL)
Expected output: Count=0
In the above query, we are retrieving all the records which have any of the NOT NULL
columns as NULL and then taking count of it. If the count is zero, this means there are no
such records and the test case can be passed.

8. ETL Testing Interview Questions
Query format:
Reconciliation Check
Select count(*)
From source table
Where list of conditions
Select count(*)
From target table
Where list of conditions
Expected output: Source count = Target count
In the above check, there are two queries, one fetching the count of total number
of records in source table and the other fetching the count of total number of
records in target table. If both the counts are same, this means that there are
equal number of records in source and target and the test case can be passed.

9. ETL Testing Interview Questions
Query format:
Relationship Check
Select count(child_id)
From( Select parent_attribute_to_be_checked parent_id,
Child_attribute_to_be_checked child_id
From( Select distinct attributes from child table
Left outer join
Select distinct attributes from parent table
On join conditions
)
)
Where parent_id IS NULL
Expected output: Count=0
In the above query, we are retrieving all the records in target table which has no parent in source
table and then taking its count. If the count is zero, this means that there are no such records and
the test case can be passed. Checking lookup condition is the most common example for this type
of check.