Proven ETL Developer Interview Questions to Assess and Hire ETL Developers

ETL Developer Interview Questions to Assess & Hire ETL
Developer
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Are you a recruiter or hiring manager? Hunting for highly
talented ETL developer?

ETL Developer Interview Questions to Assess & Hire ETL
Developer
We all know that business users, higher executives/authorities use the
data warehouse information to make important business decisions.
It’s the biggest hurdle to get the best out of the company’s
unstructured data. To overcome this real big challenge, hiring the top-
notch ETL developer onboard is a must. And believe me, it’s even
more challenging!
But don’t worry! I think, I can surely help you with this 
Here, along with proven ETL interview questions, we have written
down the detailed process to be followed in order to grab the right
talent. Let’s discuss them in detail.

Step 1: Look for Responsibilities & Skills Required for ETL
Developer
The Responsibilities of ETL Developer:
Before proceeding further, let’s understand what exactly is ETL?
ETL (Extract, Transform & Load) is the process performed in data
warehouse environment which involves the extraction of data from
multiple data sources, transformation of data into suitable format &
then loading the transformed data into destination system. In
simple words, if information is supposed to be oil, then the pipeline
created to carry that oil is nothing but the ETL process & this is
what ETL developers do! They work on creating & strengthening
this pipeline to extract & transfer the data from one place to
another.

Developer

Developer
Extract the Data (Data Mining):
ETL developer is responsible to manage & develop extraction tools
i.e. homogeneous or heterogeneous data is extracted from the
source data like relational databases, SaaS services, mobile
applications, Flat files, etc. The size of extracted data varies from
hundreds of kilobytes up to gigabytes. Extracting the data is the
toughest task amongst all & it is time consuming. Therefore all the
three tasks are performed on tandem.

Developer
Transformation /Transportation of Data:
ETL developer is also responsible to transform the data of source
into suitable format in order to meet the specification of
destination database. It involves data mapping & efficient code
generation to perform business logic.
Loading the Data:
This is the last & reverse process of extraction of data. It focuses on
how effectively & efficiently the transformed data is loaded in the
targeted system (database, file, other data warehouse).

ETL Developer Skills Required:
1. Knowledge of one or more programming languages: Python, Java, R,
SCALA. Map Reduce, etc.
2. Big Data Stores Knowledge: Hadoop, MongoDB, Spark, etc.
3. Hands on ETL Tools: Data Stage, Informatica, etc.
4. Data Modeling: The technique used for defining the detailed
business requirements for specific database in order to design the
best possible ETL process.
5. Testing Knowledge: Should be able to perform the unit testing on
generated code.
6. Analytical & Logical Thinking: A good ETL developer/ Data
engineer should be able to analyze the given data & judge all the
possible outcomes.
7. Communication skills: ETL Developer should have good verbal &
written communication skills.

Step 2: Assess Candidates Before The Interview
If you think that resumes speak the truth, then you are in a really
big trouble! Blindly trusting the resumes & asking the candidate to
directly come for the interview is risky, time consuming and a
tedious job. At the time of interview, you can gauge about
candidate’s personality, whether he/she is dedicated, passionate or
cultural fit or not. What about their skills? As an employer, you
must opt for a scientific approach to validate the technical expertise
of the candidate.
Before asking candidate to come directly for the interview, assess
their working skills using skill testing using Interview Mocha’s valid
& reliable tests that are listed here . (See the next slide)

 ETL Developer Assessment Test is designed & developed by our
subject matter experts to quantify the skills of ETL developer.
 Java Coding Test is scientifically designed to assess Java coding skills
of ETL developer
 SCALA Online Test helps employers to quantify SCALA
programming skills of ETL developer
 Python Coding Test validates Python programming skills of ETL
developer
 MapReduce Online Test helps to gauge skills of candidate for
MapReduce programming model.
 Hadoop Online Test helps recruiters & hiring managers to analyze
Hadoop knowledge of applicants.
 MongoDB Online Test is designed to quantify MongoDB, a NoSQL
Database expertise of candidate before an interview.

 Spark Online Test is created to assess Spark, a modified version of
Hadoop skills.
 Data Mining Test is developed to evaluate the working skills of
candidate for data mining
 Data Modeling Test checks candidate’s hands on data modeling
technique.
 Data Science and Analytics Test is developed to assess expertise of
candidate in extracting the data from various sources using R tools.
 IBM InfoSphere DataStage Online Test helps you to evaluate the
application skills of candidate for Data Stage.
 Software Testing Online Tests are designed to validate the software
testing skills of candidates before hiring.

For more details, you can visit Interview Mocha, an applicant testing
software. Employers can even ask for the customizable assessments.
Our content team will be happy to provide you the custom test as per
your specific needs!

ETL Interview Questions to Assess & Hire ETL Developers:
After screening the qualified candidates, ask them to appear for the
interview. Here, I have compiled the proven ETL interview questions to
ask potential prospects that will help you to assess ETL skills of
applicants.
 The models such as budgeting, financial reporting, allocations, etc.
are heavy on calculations and do they not translate well into SQL.
Among Multi-dimensional, Real Time and Relational OLAP, Which
type of OLAP is not suitable when computations have to be carried
out on these models and why?
 What do you know about Operational data store in data
warehousing?
 How is a distributed data warehouse different from a virtual data
warehouse?

 You have a product dimension and a sales fact table in your data
warehouse. A new product is created in the OLTP system and sales
transactions happen for that product and then you extract the OLTP
system. Due to this you get only the sales transaction into the staging
environment and not the products. Why did this happen?
 Can you explain me the difference between parametric models and
nonparametric models of predicting? Also given one example of
each.
 What can you say about any column if a database has high
cardinality value?
 Among fact table and a dimension table which one remains in
denormalized form?

 Shown is a Graph Database model skeleton. Consider N be the nodes
(representing entity), E be the edges (represents relationships among
entities). How do you represent entity attributes, plus metadata in
such data model?
 A business model has employee details, company details and salary
details. The model (schema) has only one foreign key i.e.
Employee_ID for all the dimensions which are necessary. What type
of model is being referred to here?
 Do you know about association rule mining? Explain with one of its
practical use case.

 Suppose i1, i2, i3, i4, i5, i6, i7 ,i8 are the items sold at a grocery store.
Customers can buy any combination of the above items as per their
requirements. After collecting the data from all transaction it was
found that i5, i6, i7 is the most frequently bought itemset. While i2,
i4, i5 is bought least frequently. What can you say about the purchase
behavior of i5i6 itemset and i2i4i5i7 itemset?
 What do you think is the primary role of a data mining engine in any
data mining systems?
 Consider data mining techniques like Clustering, Associations, Link
analysis and Deviation detection, which one would you use for
finding relationship between two entities?

 I give you the below ways that explains working of any typical data
mining process?
i) Perform ETL onto the data warehouse system. ii) Provide data
access to analysts iii) Store and manage the data in a
multidimensional DB system. iv)Analysis and Presentation of data
Can you rearrange these steps for a true data mining process?
 Suppose you're asked to reduce an existing data model using IBM
DataStage ETL (Assume you are not using Parallel Extender). Can
you do this as percentage wise reductions on the rows in the data
source? If yes, how? If no, what is the workaround?

 Why is sparse lookup in DataStage faster than Normal lookup?
 You have two time data type field values in a DataStage transformer.
In one record the value is 00:59:59 while in the other record the value
is 00:10:10. If you want add these two values so as to get the output as
01:09:09, how would you do that?
 Can you explain me about merge stage in DataStage in the context of
jobs? Also explain how is merge performed and what is mandatory
when the merge is performed on a key field?
 Among Hash file and Sequential file, which file is faster to search
data for and why?

Conclusion:
ETL is a never ending process & so are the techniques & methods
used in it! Though I have written down many aspects, role &
responsibilities of ETL developers, there may be more to this
depending upon the job-role assigned. But this guide will surely
help you to streamline your hiring process & pick up the few small
but essential things to make the big difference, to get the right hire!
If you have any queries or other approaches that worked really well
for you, we would really like to hear that. Please feel free to write it
down in comments below.

Here We Are…!
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 You can get in touch with us to know more about pre-
employment skill testing at - support@interviewmocha.com
 Visit Interview Mocha, an applicant testing software & explore
the Largest Test Library of ETL Pre-employment Tests for in-
demand skills.

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