Uploaded July 2026 | Updated September 2026, 2 hours ago
Struggling with complex SQL interview questions where you have to join a table to itself? Do you constantly get bloated row counts, messed-up aggregations, or unexpected duplicates that completely tank your query results?
In this video, we break down three essential SQL self-join patterns tested by top tech companies, reveal the one fatal mistake nearly every candidate makes, and show you when you should ditch self-joins entirely for cleaner window functions or group-bys.
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Practice these exact SQL interview questions on StrataScratch:
1) Find fare differences on the Titanic using a self join 👉 platform.stratascratch.com/coding/9603-find-fare-differences-on-the-titanic-using-a-self-join?utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
2) Trips in Consecutive Months 👉 platform.stratascratch.com/coding/2076-trips-in-consecutive-months?utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
3) Employees With the Same Salary 👉 platform.stratascratch.com/coding/9856-find-employees-with-the-same-salary?utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
📖 Full article: stratascratch.com/blog/illustrated-guide-about-self-join-in-sql?utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
🔔 Like, Subscribe, and Hit the Bell for more tech content!
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📚 Resources to Level Up Your Data Science Career
👉 Join our channel for no-BS data science advice : bit.ly/2GsFxmA
👉 Playlist for more data science interview questions and answers: bit.ly/3jifw81
👉 Playlist for data science interview tips: bit.ly/2G5hNoJ
👉 Playlist for data science projects: bit.ly/StrataScratchProjectsYouTube
👉 Practice more real data science interview questions: platform.stratascratch.com/coding?code_type=2&page_size=100&utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
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📅 Video Timeline:
0:00 – Introduction to SQL Self-Joins & Real Interview Questions
0:36 – The Core Mechanic: How Table Aliasing (`T1` and `T2`) Works
1:11 – The Row Explosion Trap: Why Unfiltered Joins Destroy Your Query
1:45 – Pattern 1 (Hard): Comparing Rows in the Same Table (The Titanic Fare Question)
2:41 – Pattern 2 (Hard): Retention, Streaks, & Consecutive Months (The Uber Driver Problem)
3:32 – Pattern 3 (Medium): Finding Shared Values & Matching Attributes (The Salary Match Problem)
4:00 – When to Stop Using Self-Joins: Using Window Functions (`LAG`/`LEAD`) & `GROUP BY` Instead
______________________________________________________________________
About StrataScratch:
StrataScratch (platform.stratascratch.com/coding?code_type=2&page_size=100&utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained) is a platform that allows you to practice real data science interview questions. There are over 1000+ interview questions that cover coding (SQL and Python), statistics, probability, product sense, and business cases.
So, if you want more interview practice with real data science interview questions, visit platform.stratascratch.com/coding?code_type=2&page_size=100&utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained. All questions are free and you can even execute SQL and Python code in the IDE. Still, if you want to check out the solutions from other users or from the StrataScratch team, you can use ss15 for a 15% discount on the premium plans.
______________________________________________________________________
📧 Contact Us: Got questions or feedback? Drop them in the comments or email us at team@stratascratch.com.
_____________________________________________________________________
#datascience #dataengineering #datascienceinterview #machinelearning #dataanalytics #sql #python #datasciencejobs #techcareers #interviewtips #codinginterview #memes #machinelearningengineer #careeradvice #datascientists #techinterviewprep #faang #trending #coding #interviewtips #interview #techhumor #ml #ai #pandas #jupyter #careerintech #datapipeline
Struggling with complex SQL interview questions where you have to join a table to itself? Do you constantly get bloated row counts, messed-up aggregations, or unexpected duplicates that completely tank your query results?
In this video, we break down three essential SQL self-join patterns tested by top tech companies, reveal the one fatal mistake nearly every candidate makes, and show you when you should ditch self-joins entirely for cleaner window functions or group-bys.
______________________________________________________________________
Practice these exact SQL interview questions on StrataScratch:
1) Find fare differences on the Titanic using a self join 👉 platform.stratascratch.com/coding/9603-find-fare-differences-on-the-titanic-using-a-self-join?utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
2) Trips in Consecutive Months 👉 platform.stratascratch.com/coding/2076-trips-in-consecutive-months?utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
3) Employees With the Same Salary 👉 platform.stratascratch.com/coding/9856-find-employees-with-the-same-salary?utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
📖 Full article: stratascratch.com/blog/illustrated-guide-about-self-join-in-sql?utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
🔔 Like, Subscribe, and Hit the Bell for more tech content!
___________________________________
📚 Resources to Level Up Your Data Science Career
👉 Join our channel for no-BS data science advice : bit.ly/2GsFxmA
👉 Playlist for more data science interview questions and answers: bit.ly/3jifw81
👉 Playlist for data science interview tips: bit.ly/2G5hNoJ
👉 Playlist for data science projects: bit.ly/StrataScratchProjectsYouTube
👉 Practice more real data science interview questions: platform.stratascratch.com/coding?code_type=2&page_size=100&utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained
______________________________________________________________________
📅 Video Timeline:
0:00 – Introduction to SQL Self-Joins & Real Interview Questions
0:36 – The Core Mechanic: How Table Aliasing (`T1` and `T2`) Works
1:11 – The Row Explosion Trap: Why Unfiltered Joins Destroy Your Query
1:45 – Pattern 1 (Hard): Comparing Rows in the Same Table (The Titanic Fare Question)
2:41 – Pattern 2 (Hard): Retention, Streaks, & Consecutive Months (The Uber Driver Problem)
3:32 – Pattern 3 (Medium): Finding Shared Values & Matching Attributes (The Salary Match Problem)
4:00 – When to Stop Using Self-Joins: Using Window Functions (`LAG`/`LEAD`) & `GROUP BY` Instead
______________________________________________________________________
About StrataScratch:
StrataScratch (platform.stratascratch.com/coding?code_type=2&page_size=100&utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained) is a platform that allows you to practice real data science interview questions. There are over 1000+ interview questions that cover coding (SQL and Python), statistics, probability, product sense, and business cases.
So, if you want more interview practice with real data science interview questions, visit platform.stratascratch.com/coding?code_type=2&page_size=100&utm_source=youtube&utm_medium=click&utm_campaign=YT+sql+self+joins+explained. All questions are free and you can even execute SQL and Python code in the IDE. Still, if you want to check out the solutions from other users or from the StrataScratch team, you can use ss15 for a 15% discount on the premium plans.
______________________________________________________________________
📧 Contact Us: Got questions or feedback? Drop them in the comments or email us at team@stratascratch.com.
_____________________________________________________________________
#datascience #dataengineering #datascienceinterview #machinelearning #dataanalytics #sql #python #datasciencejobs #techcareers #interviewtips #codinginterview #memes #machinelearningengineer #careeradvice #datascientists #techinterviewprep #faang #trending #coding #interviewtips #interview #techhumor #ml #ai #pandas #jupyter #careerintech #datapipeline
![Multiple Solutions to Data Scientist Interview Question From Amazon [Rolling Average]](https://i.ytimg.com/vi/GeJUvdkJKEc/mqdefault.jpg "Multiple Solutions to Data Scientist Interview Question From Amazon [Rolling Average]
This data scientist interview question comes from Amazon and it’s really an interesting question that deals with rolling average, the type of average that we calculate from values in a certain timeframe and we repeat it for all dates in a longer time period.
Link to the question to follow along with me: https://platform.stratascratch.com/coding/10314-revenue-over-time?python=&utm_source=youtube&utm_medium=click&utm_campaign=YT+description+link
👉 Subscribe to my channel: https://bit.ly/2GsFxmA
👉 Playlist for more data science interview questions and answers: https://bit.ly/3jifw81
👉 Playlist for data science interview tips: https://bit.ly/2G5hNoJ
👉 Practice more real data science interview questions: https://platform.stratascratch.com/coding?utm_source=youtube&utm_medium=click&utm_campaign=YT+description+link
Timeline:
Intro: (0:00)
Interview Question: (0:28)
Framework to solve the problem: (1:40)
Understand your data: (2:36)
Formulate your approach: (6:12)
Common table expressions and interval function: (7:09)
Window Function Approach: (20:35)
Comparison of approaches / Optimization discussion: (25:45)
Conclusion: (28:08)
About The Platform:
Im using StrataScratch (https://platform.stratascratch.com/coding?utm_source=youtube&utm_medium=click&utm_campaign=YT+description+link), a platform that allows you to practice real data science interview questions. There are over 1000+ interview questions that cover coding (SQL and python), statistics, probability, product sense, and business cases.
So, if you want more interview practice with real data science interview questions, visit https://platform.stratascratch.com/coding?utm_source=youtube&utm_medium=click&utm_campaign=YT+description+link. All questions are free and you can even execute SQL and python code in the IDE, but if you want to check out the solutions from me or from other users, you can use ss15 for a 15% discount on the premium plans.
Contact:
If you have any questions, comments, or feedback, please leave them here!
Feel free to also email me at nathan@stratascratch.com
#AmazonDataScientistInterview")
![Solving an Airbnb Data Science Coding Interview Question | SQL Interview [Fav Host Nationality]](https://i.ytimg.com/vi/IKw0lkmBHNI/mqdefault.jpg "Solving an Airbnb Data Science Coding Interview Question | SQL Interview [Fav Host Nationality]
This SQL data science interview question was asked by Airbnb. I’ll cover both the question and answer and give a detailed explanation of the approach. I walkthrough each step of my answer, assumptions, approach, and explain every line of code I write. This is literally how I would answer every data science interview question and prepare for every data science interview at FAANG companies and others.
Link to the question: https://platform.stratascratch.com/coding/10073-favorite-host-nationality?python=&utm_source=youtube&utm_medium=click&utm_campaign=YT+description+link
The question has many concepts that are always tested during a data science interview. This SQL interview question requires 3 JOINs and 2 subqueries. There are some tricks tested where you have to identify the highest review score using the SQL max() function. And lastly, this coding interview question tests your knowledge on how to de-duplicate data.. This question covers concepts that are commonly found in data science interviews at Facebook and Google.
This series is for both beginner and intermediate data scientists and analysts interested in learning how to solve common data science interview questions in SQL. These are real data science interview questions. For some background context and an intro about what this series is about: https://bit.ly/36kKbxG
👉 Subscribe to my channel: https://bit.ly/2GsFxmA
👉 Playlist for more data science interview questions and answers: https://bit.ly/3jifw81
👉 Playlist for data science interview tips: https://bit.ly/2G5hNoJ
👉 Practice more real data science interview questions: https://platform.stratascratch.com/coding?utm_source=youtube&utm_medium=click&utm_campaign=YT+description+link
Timestamps:
Intro: (0:00)
Interview Question: (0:10)
Explore Dataset: (0:35)
Writing Out Approach: (01:57)
Coding The Solution: (4:40)
2nd Solution!: (10:41)
About The Platform:
Im using StrataScratch, a platform that allows you to practice real data science interview questions. There are over 1000+ interview questions that cover coding (SQL and python), statistics, probability, product sense, and business cases.
I created this platform because I wanted to build a resource to specifically help prepare data scientists for their technical interviews and to generally improve their analytical skills. Over my career as a data scientist, I never was able to find a dedicated platform for data science interview prep. LeetCode and HackerRank were the closest but these platforms specifically serve the computer developer community so their questions focus more on algorithms that working with data.
So, if you want more interview practice with real data science interview questions, visit https://platform.stratascratch.com/coding?utm_source=youtube&utm_medium=click&utm_campaign=YT+description+link. All questions are free and you can even execute SQL and python code in the IDE, but if you want to check out the solutions from me or from other users, you can use ss15 for a 15% discount on the premium plans.
Contact:
If you have any questions, comments, or feedback, please leave them here!
Feel free to also email me at nathan@stratascratch.com")
