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🔥 SQL Based SFMC Interview Questions Part - 1
1. How do you remove duplicate records from a table in SFMC?
Answer:
I usually deal with duplicates inside Data Extensions. I handle this using SQL queries in Automation Studio.
What I personally do is use ROW_NUMBER() with a partition. This helps me identify duplicate records based on a key like email.
For example, I write something like:
I partition by Email Address
I order by a field like Created Date
Then I keep only the first record
This way, I make sure I keep one clean record and remove the rest.
2. What is a subquery, and how do you use it? (Asked In Deloitte Interview)
Answer:
A subquery is basically a query inside another query. I use it when I need to filter data based on another result.
In SFMC, I often use subqueries when I want to target a specific audience.
For example, I might say:
I want all users
But only those who have made a purchase
So I use a subquery to first find customers who purchased, and then filter the main data using that.
It helps me make my segmentation more precise.
3. What are window functions, and when do you use them?
Answer:
Window functions are very useful when I want to perform calculations across a group of rows without grouping them completely.
So, I mainly use them for:
Deduplication
Ranking
Finding latest records
For example, I use ROW_NUMBER() to rank records for each customer and pick the latest activity.
I find window functions super helpful when I want advanced logic without losing row-level data.
4. How do you handle NULL values in SQL? (Asked In TCS Interview)
Answer:
In SFMC, I often see NULL values in Data Extensions, so I handle them carefully.
What I usually do:
I use IS NULL or IS NOT NULL to filter
I use functions like ISNULL() to replace NULL with default values
For example, if a field is empty, I might replace it with “Unknown” so my data stays clean.
I always make sure NULL values don’t break my segmentation or logic.
5. What is the difference between INNER JOIN and LEFT JOIN? (Asked in Capgemini and Augment-ix Interview)
Answer:
I use joins a lot in SFMC when combining multiple Data Extensions.
INNER JOIN: I only get records that match in both tables
LEFT JOIN: I get all records from the left table, even if there is no match
For example:
If I only want users who have orders → I use INNER JOIN
If I want all users, even those without orders → I use LEFT JOIN
I usually prefer LEFT JOIN in marketing use cases because I don’t want to lose audience data.
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Thanks for reading the post!
Until Next time,
Gourav
Founder @ TheSFguy