Data Science SQL Interview Question Walkthrough (real interview style) | SQL Sundays #8

Hi friends! Welcome back to SQL Sundays! A weekly SQL data science interview questions and answers walkthrough.

This is another data science SQL interview question and answer done from beginning to end in a real interview style.

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Check out StrataScratch for data science interview prep:

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Hi, my name is Tina and I'm a data scientist at a FAANG company. I was pre-med studying pharmacology at the University of Toronto until I finally accepted that I would make a terrible doctor. I didn't know what to do with myself so I worked for a year as a research assistant for a bioinformatics lab where I learned how to code and became interested in data science. I then did a masters in computer science (MCIT) at the University of Pennsylvania before ending up at my current job in tech :)

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Music Credit:
TheFatRat & Laura Brehm - We'll Meet Again

[DataProfessor]

Thanks Tina for another awesome SQL lesson 😊

[ayushmore]

Have been binge watching all the SQL Sundays now in preparation of interviews! Thanks for all the content!

[BABartz]

This playlist is the reason I subscribed. Please do more. Excellent format.

[zihonghuang]

Thank you so much Tina. I have watched all sql videos and have learnt a lot, esp learn about how to prepare a question before writing the queries. Thxxxx

[kaoutarbentalha]

hey, Thank you so much for this awesome SQL playlist, please do more

[bballlover]

Thanks Tina! Really loved this series, can you do more again?

[dehan]

Thanks Tina I finished learning all these 8 questions, thinking about purchasing the Stratascratch membership. I will succeed in the tech interviews!

[danielw]

Hi Tina, thanks for your walkthrough, and here's my soln about the ntile. Correct me if it's wrong because I just start to break into the data science field. Thanks :)

select
from_user,
count(*) as total_email,
percent_rank() over (order by count(*) desc) as ntile
from google_gmail_emails
group by 1

Also, would love to hear your opinions on what do you think about the difference between CTE and subquery in terms of efficiency? And what are the optimization tips would you say in writing something like hundred lines of SQL code?

[thevoiceofb]

Hi, great video, thanks for sharing! I'm just left wondering how are you able to use an aggregate function with a window function in the same select? I thought that should not be possible

[prathameshbane]

Please upload videos on SQL Sunday interview questions! Thanks for the content... Happy Learning!

[jariuslouie]

SQL wednesdays :) Thanks Tina. As usual, very helpful video. I wouldn't mind if you placed an ad or two. Not skipping ads might be the only way for me to support you and your channel right now aside from watching, liking and sharing your vids.

[siyangzhou]

Thanks so much Tina for preparing this AWESOME series of SQL interview questions! Wondering if you have any plans of posting similar interview prep series for Python in the future?

[shanefan]

just learned group by 1 from you nice solution

[ericzheng]

The answer provided by StrataScratch is fishy because it uses NTILE(100). It already assumes that there are only 100 records in the table, and it tries to divide these 100 records into 100 groups so that every record has its own ranking number. AND thanks Tina for letting me know rank functions are also called window function!

[agrim]

Tina plz make more videos on sql plz your videos are really helpful.🙏🙏🙏🙏

[xuzhang]

Thanks for sharing. Question on the solution Ntile(100), there is a chance to assign the same percentile to the same number of emails? say there are 101 rows and the 1st two rows have the same number of email.

[로그-vi]

Awesome!! I liked your approach better.
When you do group by 1, is that grouping by the user ? (I’m still learning SQL haha)

[shanminlin]

subscribed to stratascratch through your link!

[drraxinarc]

Dw, imma save this to my playlist so that I can watch this Sunday to maintain the Sequel Sunday regime😉

[meanrambler]

A SQL newbie here.. Can anyone help me where I can find such questions for practice??🙄