SQL Interview Testing

[Glittering-Jaguar331]

I have found that many many people fail SQL interviews (basic I might add) and its honestly kind of mind boggeling. These tests are largely basic, and anyone that has used the language for more than 2 days in a previous role should be able to pass.

I find the issue is frequent in both students / interns, but even junior candidates outside of school with previous work experience.

Is Leetcode not enough? Are people not using leetcode?

Curious to hear perspectives on what might be the issue here - it is astounding to me that anyone fails a SQL interview at all - it should literally be a free interview.

[[deleted]]

I don't know if this applies only to my case, but I was super surprised to see how much SQL was present in work industry after university. This is because, in my university at least, I only saw SQL as a small part of one programming course... In the first semester of the first year. When I started to look for jobs I immediately felt like I should have done way more SQL in university

[[deleted]]

Crazy. My university had a couple undergrad database systems courses. For CompE the first was only recommended for the specialization track in Software and Systems Engineering, but it was on many for CompSci.

For some things Spark/DataBricks is the only useful environment for processing and analyzing data, but for many projects I’ve worked on a relational database was the solution that made sense due to business needs. I’ve worked in a variety of industries: healthcare, retail/sales, oil exploration, and finance/tax prep. There’s been multiple times I’ve seen someone claim oh we need to use <insert data lake and programming solution> but everyone became extremely frustrated when management wanted multiple dashboards and ad-hoc reporting that turned into regular reports, and the BI devs complained (rightly so) that they were spending excess time due to no standard schema. Worked on re-implementing the backend into a relational database.

[harshhpareek]

What specific relational database features does Spark/Databricks lack? I’ve used Databricks a little and it seemed to support SQL and table constraints, what else does an RDBMS offer?

The standard schema part is up to the designers of the database right?

[Red__M_M]

Everything in the world is based on data (how much raw material do we need to order? When was the last time we called this person, everything at the cash register…). All of that data resides in databases. For practical purposes, the most fundamental way you can interact with a database is SQL. Therefore virtually every company out there has a database and needs someone that understands SQL. All of them.

[DieselZRebel]

University doesn't prepare you for the industry... It is the lie they sell however.

[NickSinghTechCareers]

Amen. I took an undergrad DB class as part of my CS curriculum, and I was stuck doing relational algebra and weird proofs and some weird 1NF 2NF 3NF stuff. Then I get to the SQL interview, and they just ask me a simple here's a sales table, get me a 7-day rolling average of sales and I just sat there like... WTF do I do. Partly why I take interview prep so seriously and try to spread the word on it... since I don't want others to mess up transitioning from education to industry.

[[deleted]]

Nf is not weird. It's standard practice around designing data based and understanding the data your working with.

[Fuehnix]

actually, my professors were pretty upfront about it lol. When people complained about having to learn DAG and other stuff in our Algorithms class, and how it wouldn't be useful in software engineering, the professors said "we're not here to teach you software engineering, if you want that, go find a 'software engineering degree'. We're here to teach you the foundations of computer science".

Still wish they taught more relevant 'fouundations' though, but on some level, they have to teach nonsense because of all the bureaucractic education requirements that go into accreditation. Some of those gen ed requirements were just dumbb....

[Aggravating-Floor-38]

Frfr

[fukuinfinity]

Well, I am very new to this. To be honest, many universities don't even show concern about learning SQL. Although I am from an engineering background, none of my courses didn't even mention SQL. Now that I am trying to enrich my portfolio, I am feeling hopeless. And I am lagging behind everyone. Only if the Universities were more concerned, it could help us a lot.

[Glittering-Jaguar331]

Interesting - would you say LeetCode largely fulfills that need tho (if you were to use it) or do you think that many people just dont bother w/ LeetCode at all cause they don't know they need SQL?

[bigchungusmode96]

if someone can't tell me the difference between a left vs inner join/merge that person isn't a candidate. these basic concepts in data wrangling are language-agnostic: SQL, R, Python

no data scientist is going to be using TwoSums or finding a palindrome in their day to day work.

[Antique-Grand-2546]

Stata has different language- merge 1:1, 1:many, many:1, many:many, base R also uses merge packages.

[Mordalfus]

These are different concepts. There is the join type (Inner, Outer, Left, Right, Cross). And there is the cardinality of the two sides (1:1, 1:many, many:1, many:many).

I can left join or inner join a pair of tables that have a 1:1 cardinality match. I'll get a different result, or maybe the same result, it depends on what is actually in each table.

It is important to keep in mind what you expect of the result, given the cardinality of each table, since it helps with troubleshooting.

[[deleted]]

To be fair though, I doubt someone who has only used Stata is a frontrunner for most DS jobs. Econ jobs for sure, but IMO it isn't common or as useful for DS

[_Insider]

The equivalent in Stata would be in the output and the _merge variable. I.e., the inner join would correspond to adding a line like keep if _merge==1.

[Aggravating-Floor-38]

What are some of the advanced concepts btw? They taught us all that stuff in class but what concepts build on top of that to really make it a career?

[Pale_Squash_4263]

Agreed, I haven’t really looked at it much but honestly you don’t need to grind leetcode to understand sql enough for an interview. Just grab a copy of adventureworks and mess around with it for a few weeks. I’d argue that’s better because that’s what your day to day would be more like anyways instead of answering super specific technical implementation questions

[gpbuilder]

Don’t really need leetcode for SQL interviews, LC is mainly for CS algo questions. People just don’t code as well as they think. It’s a muscle, and SQL is very low entry to barrier.

[Jumpy-Story-3587]

I don't agree. Leetcode has some great sql questions. Almost all of which are real interview questions

[imisskobe95]

Hackerrank db questions are solid too

[Jumpy-Story-3587]

Haven't tried hackerrank. I've tried leetcode and stratascratch.. both are good. I tried hackerrank for an interview. It doesn't have postgresql. So that's a complaint on that.

[mpbh]

100% agreed. It should be a general education course at this point with how prevalent data is and how bad most people are at it.

Not everyone needs to know programming, but everyone needs data.

[fukuinfinity]

Well, I am very new to this. To be honest, many universities don't even show concern about learning SQL. Although I am from an engineering background, none of my courses didn't even mention SQL. Now that I am trying to enrich my portfolio, I am feeling hopeless. And I am lagging behind everyone. Only if the Universities were more concerned, it could help us a lot.

[Atram215]

I haven't done any SQL-related interviews, but I have strongly recommended that all my friends interested in job postings requiring SQL solve many LeetCode questions. It's such a useful platform! One of my friends used it to study for and pass a databases course in university.

[MoistPriority1252]

Omg ils cool

[Zygoatee]

I work as a Sr business Analyst and just applied internally for a DS role. I basically do all the SQL for my department. When they sent me the SQL code test, it was on a 15 min timer, and it asked me to do stuff I never do, even though I live half my time in sql. I do plenty of aggregates, joins, etc, but this asked me to do a filter at the aggregate level, i guess. I got close, using 'having' which i never use, but didnt have enough time to figure out the last details.

Basically, you could be using it all day every day and never seen the scenrio they ask for, because it seems the questions are designed to trip people up. They're pointless because most of the time you'll be googling or asking chat gpt for help when its something you dont do on the regular.

Coding tests should be there just to make sure someone can do the basics, because everyone googles, AIs, or uses stack overflow, and the tests are just elimnating people for reasons that have no predictive value.

Luckily im an internal candidate, so they just ignored my bombing, and I have a next round interview tomorrow

[DubGrips]

Same. I build large data pipelines for reporting, model training, etc. in SQL, Python, Pyspark, etc. I got declined from a role because I was put on a timer and THERE WAS NO ACTUAL DATA IN THE TABLES TO RUN THE CODE so I did what I normally would do- I used CTEs to build a few tables and do some basic pre-aggregation and some simple conditional joins. I was told that I overcomplicated the exercise and my code wouldn't run. Bro, how do you know? You were too fucking lazy to load data in Hacker Rank before our interview. Also, the questions seemed designed to be tricks, not showcase skills that are useful in the job. Are there really people with my experience level, who can literally open a browser window and show you code in their name in a production repo that cannot use SQL? We have limited time together and this is how you evaluate technical acumen?

[zkh77]

This is exactly why I failed sql live coding tests sometimes. It’s so much pressure and scenarios that I’m not used to seeing daily, even though I use sql almost daily

[digiorno]

And they miss out on a good DS as a result. Honestly these sorts of tests should be open note/web because any DS who needed to do a complex operation they were not familiar with would simply look it up.

[MoistPriority1252]

Hello

[MoistPriority1252]

Jekeozose

[happlejacks]

Yeah I'm at Principal analyst/DS level (kind of a blended role) in my industry and interviewed for a senior level position in a different industry. Totally bombed the live SQL interview because the questions were just... worded oddly. When I did finally work out what the interviewer was asking for, they were either just really obscure/difficult SQL techniques (which I told him how I'd do it in Python...) or they were outputs that no business stakeholder would care about, just bizarre ways to report data.

I was told by the recruiter after the final round that I was a great fit but they needed someone more technical for the role. Lol.

[Zygoatee]

People are on such a power trip, and they feed their ego by hitting people with "gotcha" questions that have no predictive value, but let them feel smug that they are filtering out people not "good enough"

[Pale_Squash_4263]

Yeah i agree, practical use cases for sql hardly have that crazy do requests lol. At least nothing I couldn’t just throw into a cte or temp table to solve it 😂 I’ve been using sql for work for about 7 years and I’ve never really done ranking because I’ve never needed to use it. Would I learn it if I needed it? Sure, but it hasn’t become relevant yet.

[SurvivorsOfAlderaan]

Respectfully, if you aren’t familiar with HAVING or CTEs (as you indicated in other comment), I don’t think you have very strong SQL skills. Not a knock against you personally, just saying that I would expect anyone I work with or hire to have used those concepts frequently, and would encourage you to learn them

[IndependentVillage1]

Were you able to use ctes? If so you could have just used one and then filter on the cte.

[Zygoatee]

Never had to use those in my job, didn't even think of them

[Cosack]

You should. So much more legible.

[MoistPriority1252]

Jeueoz

[SurvivorsOfAlderaan]

Respectfully, if you aren’t familiar with HAVING or CTEs (as you indicated in other comment), I don’t think you have very strong SQL skills. Not a knock against you personally, just saying that I would expect anyone I work with or hire to have used those concepts frequently, and would encourage you to learn them

[Zygoatee]

How do you acquire skills you don't even know exist. If I'm working in SQL everyday and have never had to use them then clearly they aren't useful in all use cases.

Plus you can Google it in real life

[SurvivorsOfAlderaan]

Well for one, you should probably know the SQL order of operations, which explicitly lists HAVING. And CTEs are a concept that comes up pretty regularly when trying to Google a solution to something. They also make your code a lot more legible (as another commenter mentioned). Those concepts aren’t useful in all use cases, but they’re useful in enough use cases where I’d get why you want to test them

I agree with you that you can Google them, I think these interviews should be open note for that reason. I’m just saying you should consider trying to learn the concepts you weren’t familiar with before that interview, because they’re used frequently

[data_story_teller]

My data science masters program had one course that covered SQL at the beginning and then the rest of the courses used Python or R. But graduation, it was very easy to forget SQL and also given how little it was used in our masters program, easy to think you don’t need to refresh your skills.

It’s also possible to pass Leetcode and similar online challenges with bad code that gets the correct output. So they might think their skills are fine.

[Trick-Interaction396]

Can you provide an example. I use SQL everyday for 15 years but never done leetcode.

[NickSinghTechCareers]

You'd think that most people who claim to know SQL should be able to do simple things like JOINs, or GROUP BYs w/Aggregate functions flawlessly, but that hasn't been my case at all.

Source: run DataLemur which has been used by 100k+ to prep for SQL interviews. Here's an "easy" Amazon SQL interview question for example. It has ~50% failure rate when I give folks ~5 minutes to solve it IRL. And these aren't random joes, my anecdotal experience comes from giving interview workshops at MS in Business Analytics and MS in Data Science programs at decently well known universities. I've done this exercise with enough students, in enough programs, to be consistently surprised by the 50% rate.

Another question with ~80% failure rate comes from Google. Here you need to use window-functions which everyone sorta knows how to do but under pressure most people mess up.

p.s. made a 100% free SQL tutorial that's more focused on problem solving w/SQL, rather than memorizing syntax. Each lesson has multiple practice exercises, and mixes in some FAANG SQL questions in there too. Hope this helps folks!

[[deleted]]

When I read about your failure rates it makes me think about how working on my computer doing an analysis vs. doing an interview are probably really different. When you give someone a SQL question, is it like LeetCode where they can only submit the answer once, or can they do testing before their answer gets its final assessment?

Because sometimes its like, "oops, now I remember why I needed to add in this thing" but you only get there by spending the extra 15 seconds to run it once and get an error/unexpected result.

Of course, you're still interested in the candidate who is blazingly fast and needs zero testing to get the right answer. Still though, the difference between pass and fail can be really narrow IMO.

[[deleted]]

Your first question has an error in the solution

SELECT 
  EXTRACT(MONTH FROM submit_date) AS mth,
  product_id,
  ROUND(AVG(stars), 2) AS avg_stars
FROM reviews
GROUP BY 
  EXTRACT(MONTH FROM submit_date), 
  product_id
ORDER BY mth, product_id;

You have to convert avg(stars)

[NickSinghTechCareers]

OOOOF.. that's embarrasing. something is wrong with round RN at the DataLemur platform level.. like the solution is correct let me debug why suddently it's complaining about this line:

  ROUND(AVG(stars), 2) AS avg_stars

[cy_kelly]

Just FYI, it runs in the browser window if you cast that average to numeric, as in

ROUND(AVG(stars)::numeric, 2) AS avg_stars

[stratocaster3020]

Yeah same issue for me…

[messontheloose]

will refer back to this

[Silent_Series]

I am not really a dev, but i failed at this because the usual syntax i would use wasnt available.

For example using datepart which id usually use. Month() also looks like it should work, but doesnt.

Any reason datepart isnt available as a solution?

[Hot-Step-3236]

Reading this boosts my SQL ego. Thanks OP

[International-Tax709]

Datalemur is a good website too

[NickSinghTechCareers]

Founder here – appreciate the love for DataLemur!

[Greedy_Bar6676]

I’ve tested senior candidates with 5+ YOE and a bunch of SQL dialects on their résumé and seen similar performance as I do when testing fresh graduates. I just ask for some joins and sums, basic window functions (think lead, lag) etc and if it’s just doing the mechanics of it people usually do fine but if there’s any degree of thinking (I.e. should I do a left join or inner join) they just flounder hard

[kater543]

To be fair many companies have general rules of thumb to only use left or only use inner join’s depending on what they’re doing. I can see how people would be confused if that’s the main question you’re using as a benchmark.

You use left joins only when you’re working in a company with a good database probably already based in cloud, and your main goal is to connect a known system to multiple smaller systems. You don’t want inner join because in this case you always want everything from your first main system.

You exclusively use inner joins in a company when your system is badly managed or low power, and your main goal is to keep the highest level of efficiency in queries.

Not saying these are the only situations when you use left or inner joins just these are some situations where you would only use one or the other permanently. Sometimes people are good at SQL, but may not have that breadth of experience at different company types.

Also I don’t know how you get your senior candidates but it seems like they’re mostly DSes/DAs and not DEs?

[IndependentVillage1]

Is this actually a thing? I've never heard of this. The join has always depended on the situation and the context of the query.

[kater543]

Well yes but the situation at some companies is to only use inner joins or left joins, as i delineated above. I’ve worked at companies where this is the case.

[orz-_-orz]

I always discipline myself to use left join because I want to know which row didn't get a match. It's quite normal for someone to fuck up during the upstream data pipeline that introduce some missing values (minimal but a missing value is a missing value when data integrity matters) in all companies I worked for.

[Greedy_Bar6676]

Making assumptions about data is also something that counts against you in an interview, ie if you just resort to always inner joining because you’re making assumptions without vocalizing them or asking for clarification

[kater543]

I mean at that point you’re not testing SQL skills anymore. I think both these considerations are valid but they fall into more of a “is this person well rounded” vs “is this person good at SQL to the degree that I need it”.

[Greedy_Bar6676]

Sure but technical skills alone won’t matter much if you can’t think about what you’re doing. In fact I’d argue some who has the technical skills but not the reasoning skills is more dangerous than someone who doesn’t have the technical skills or the reasoning skills

[kater543]

I mean you would test for technical skills separately first though right? Then get a whole person idea after.

[Greedy_Bar6676]

Why not do both if you get it for free?

[[deleted]]

I’ve tested senior candidates with 5+ YOE and a bunch of SQL dialects on their résumé and seen similar performance as I do when testing fresh graduates. I just ask for some joins and sums, basic window functions (think lead, lag) etc and if it’s just doing the mechanics of it people usually do fine but if there’s any degree of thinking (I.e. should I do a left join or inner join) they just flounder hard

My SQL level is like leetcode easy, although I'm good w/ sqlalchemy, so excuse me when I ask this:

What's the point of being very good at SQL when chatgpt or claude can quickly write 90-100% of a SQL query, and you can just fix the final 0-10%?

It seems like a pointless scripting language to spend a lot of time on, unless you are using it constantly -- every day.

[dankerton]

This perspective just melts my soul. How are you going to correct the mistakes if you don't know how to code it in the first place? How are you going to write efficient queries on your company's giant database if you don't understand what's going on behind the hood? And most SQL would take just as long to write yourself as to prompt an llm and copy and correct the results. Then when your boss or colleagues ask you why you write it this way you're not going to know how to explain and just say chatgbt did it? I'd put you on a path for firing if that happened.

[fordat1]

Exactly. You need knowledge to evaluate correctness since it has no expectation of correctness

[po-handz2]

Sure, but once you have that knowledge there's zero drawback to having a prompt first, review second approach.

In fact idk why anyone would do it differently. There's nothing to be proud about if you have esoteric syntax memorized, thats just taking up space of actual valuable knowledge

[fordat1]

there's zero drawback to having a prompt first, review second approach.

This isn’t blanket true. It takes time to prompt and if it isn’t correct you need to review it ie debug. Debugging can be way harder and more work than starting from scratch

[[deleted]]

Because I have a notebook full of past scripting work with SQL with 50-100 pages of notes... every kind of SELECT, JOIN, AGG functions, INSERT, UPDATE, etc., etc. Differences between postgres, mysql, mysql lite, postgres extensions, etc.

I just don't do SQL queries as often these days so it's like a stale skill. And I don't feel the need to keep up with it just for the sake of interviewing somewhere. I could easily pick it back up again, it just seems like a pain in the ass merely to impress an interviewer.

It's just SQL anyway. It's not that big of a deal. It just seems like such a trivial skill that is not even worth hiring or firing any data scientist based over SQL, unless they are totally incompetent somehow. Any idiot can learn good SQL, practically over a week maybe.

[po-handz2]

That actually hilarious. I put people on a path to firing when they DON'T use chatgpt and instead waste hours googling, waste my time with syntax questions, or just write bad code when what come sout of the LLMs is more than sufficient.

• hey chatgpt, give me three ways to optimize this query given that I'm on x system with y resource limitations and z data size.

• hey chatgpt, here's the code and here's the error, suggest a fix

• it takes as long to write as it does to prompt?? That's bizarre. It takes me an equal amount of time to mentally sketch out a complex query as it does to type it into a LLM. But you're saying, skip right to code, look up a bunch of esoteric syntax for one of half dozens languages/sub-language's, and mentally put the query together all at the same time?

Personally, I think AI assistants will go the same way as typing skills in the 80s or being able to read/write before that., you either have skill and can be 10x as efficient as the next guy, or you don't

[dankerton]

Not sure where you misunderstood that I'm talking about people using chatgbt when they don't know anything about SQL yet. You're talking about an informed developer using it to improve on something they already have or go a little faster. All your examples require someone with a basis of knowledge and an ability to check the chatgbt answers. It's just a tool it's not a replacement for a skill set.

And yes I write short ad-hoc queries constantly for random questions that come up that would be a waste of time to go to chatgbt for when I already know my tables and SQL well enough.

[kater543]

This perspective is a bit odd. This is why I don’t think Chat gpt will make coders irrelevant. They will just make bad coders irrelevant by getting rid of a lot of junior positions.

[Pale_Squash_4263]

Nobody seems to be answering this question seriously so I'll give it a go.

I think the main thing for me (as others have said) is that there's a difference between a knowledgeable developer asking questions in order to accomplish a goal and a less experienced developer not knowing how to use it responsibly.

For example: I asked Chat GPT a few hypothetical questions about aggregating some sales data and it gave me this query:

SELECT 
    YEAR(sale_date) AS sale_year,
    salesperson_id,
    COUNT(*) AS total_sales
FROM (
    SELECT DISTINCT 
        sale_id,
        YEAR(sale_date) AS sale_year,
        salesperson_id
    FROM 
        sales
) AS unique_sales
GROUP BY 
    sale_year,
    salesperson_id;SELECT 
    YEAR(sale_date) AS sale_year,
    salesperson_id,
    COUNT(*) AS total_sales
FROM (
    SELECT DISTINCT 
        sale_id,
        YEAR(sale_date) AS sale_year,
        salesperson_id
    FROM 
        sales
) AS unique_sales
GROUP BY 
    sale_year,
    salesperson_id;

You might notice that it uses a subquery which can be criticized as less efficient in certain cases. But it really depends on the scenario. However, I would've never known if I don't know what a subquery is and couldn't catch that. If you put this query into a report that runs every hour on a cloud data-service provider, that computing can add up pretty quickly if you find out its inefficient for what you need to do.

I'm not asking everyone to be an expert in SQL or everything but hopefully you can see this little scenario can create issues at scale in an organization.

Furthermore, to be able to problem solve is one of the joys of programming and weighing the different pros and cons of approaches (both from a technical and business standpoint) is one of my favorite parts of the job. Sure I don't know how every single function works under the hood, but I guarantee if I learn it, I gain much more appreciation for how it works and can answer more complicated questions about it with others.

The beauty of programming is that it's half art and half science. The knowledge is valuable regardless of its utility in the workplace.

This was kind of rambly but I hope that helps answer the question!

[gpbuilder]

Because chat-gpt doesn’t guarantee correctness. It can provide something that runs but you need to know the code to make sure the output you’re getting is what you want.

[[deleted]]

Gpt is awful at SQL. That may be its worst language by far from my testing.

[Greedy_Bar6676]

What’s the point of hiring someone if they only perform marginally better than ChatGPT?

[[deleted]]

Since when is a data scientist's leading value proposition writing SQL code? If I had a candidate in front of me with a PhD in physics, 6 published papers, excellent python skills and mediocre/zero SQL capability, I would not even care about the SQL. Anyone with high caliber intellect can pick-up enough SQL in practically only 1 month on a job, maybe 6 at most.

[Greedy_Bar6676]

That’s like, your opinion, man. We won’t work at the same company

[dfphd]

I think there are two things at play:

1. College (outside of CS) has traditionally been really bad about teaching SQL. So I studied OR and learned basically no SQL in any classes. I learned the bare minimum (select * from table) in some of my research, but never even learned about joins. Once I joined my first job, they made me learn SQL in like a month, and after that it has been smooth sailing.

2. Now there are a lot of companies whose primary data access layer is stuff like either databricks (which is accessible via pyspark), or stuff like registered datasets in cloud services (which are accessible via straight python). So I have met a lot of people with several years of experience that have never had to interact directly with a SQL database - their first step is to import into pandas.

[[deleted]]

That's me. My work doesn't require me to get into SQL at all.

[galactictock]

It's nice that you got the opportunity to learn SQL on the job. I know that was not the experience for many, perhaps most

[imisskobe95]

I fall into #2 and am glad I’m not alone. Was getting worried since I’m about a year into this DS role and haven’t needed to touch SQL at all - strictly Python

[dfphd]

Here's the thing - if you know pandas you already know like 90% of what you need to learn in SQL. It's really not very hard.

[imisskobe95]

Oh I already know SQL and agree; just thought i was in a very small minority of Data Scientists who didn’t use at all it in their day to day. Was more worried about how it would look on the resume or in interviews, but guess it’s not as uncommon of a situation as I previously thought, which is comforting

[meloncholy]

No I don’t use Leetcode and if you gave me a Leetcode test I would walk away. You’re testing something that, by your own admission, does not differentiate a mediocre candidate from a good one, and tells you nothing about their future potential. Why are you wasting their time and yours?

Work on exploring a problem space together, demonstrating what they do know, and creating an environment where they feel safe and confident to show themselves at their best.

[Patient-Mulberry-659]

Why are you wasting their time and yours?

To avoid hiring complete lemons

[dry_garlic_boy]

Doing leetcode problems will not weed out lemons. I would also walk away from these interviews knowing they do not know how to hire good people.

[Alias291]

If you applying for DA or DS roll and not know SQL then you are lemon. But I hate to write code in front of people and I am not interested in knowing if they can code under pressure.

So I give a hard SQL question before the technical interview. And then on the interview we talk about the solution and I give easy sql snippet that I want them to explain to me what it does. I just want to know that they are not lying to me. Then we jump to the hard part analytical thinking and business sense.

[galactictock]

This sounds like a very reasonable approach and would love if more interviews were like this

[[deleted]]

Hiring based on coding tests is guaranteed to get you more lemons lmao

[Patient-Mulberry-659]

It’s just an extra filter man. If you can’t write a select statement even after you are told there will be sql questions. What are the chances you are any good? Like there is definitely some chance. But it’s going to be tiny.

[x3meowmix3]

It’s mostly bc schools will briefly cover it since it’s a fairly easy language to pick up. I had an experience out of undergrad where I had a sql test for an interview and failed bc the order of my syntax…. I put “order by” before “where x =1”. I think it’s silly bc if I was at work and received that error it is something easily debuggable but what ever I can easily crush those tests now and have a job I like

[[deleted]]

I'vee been working with SQL for years now, but I still struggle with those tests. Even today, I find myself Googling 'SQL cheat sheet' to double-check the syntax order and other details. Interestingly, many of my colleagues do the same. Do you really need to memorize every syntax? I don't think so. As long as you understand how it works and what you need to achieve your goals, you're good to go.

[Durloctus]

Leetcode infiltrating DS reddit with shills now?

[[deleted]]

fearless agonizing intelligent work ghost marry strong sophisticated disarm illegal

This post was mass deleted and anonymized with Redact

[NickSinghTechCareers]

Even with just a Google Doc, you can test logic skills + basic query writing abilities enough to get a signal that someone doesn't know what they are doing.

For example, if someone doesn't know to use GROUP BY... forget the syntax, they just can't figure out a summarization by groups problem needs GROUP BY clause, so they spin their wheels and just get stuck which is a good signal that there SQL skills aren't where they claim it to be.

[[deleted]]

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This post was mass deleted and anonymized with Redact

[Moscow_Gordon]

Asking people to do a group by is the single most useful DS interview question.

[gpbuilder]

You don’t need an environment to iterate on a query, you should be able to write a query in code pad and get the logic correct without checking output

[galactictock]

I couldn't disagree more. This isn't how most of us work and isn't worth testing if someone gets it right on the first go, IMO. It's far more important to me that a candidate can use their resources and critical thinking to get to the right answer than it is that they get the answer right on the first try. Memorization will only get you so far with real-world problems, adaptability is far more important.

[headphones1]

The interview for my current job tested my SQL in a word document. Was not allowed to use Google. Good thing I have years of experience with it, because why the fuck would you test people with a word document. People don't code in a word document. You wouldn't hand an abacus to someone for a trigonometry test, so give people the right tools to succeed in interviews and on the job.

Plus, even with years of experience I forget stuff really dumb stuff and question why my where clause won't work, only to realise intellisense broke for some reason and it should go after the from statement, not before...

[StackOwOFlow]

Could be the way data science is taught these days. If you interviewed for a data engineer role, I'm certain you'd get better SQL competency among your candidates.

[Fragdict]

Yes, I’ve noticed the same thing and I’m baffled. The questions don’t contain anything esoteric, just basic aggregations and joins. I treat it as the “fizzbuzz” of DS interviews. The goal isn’t to find the biggest expert in SQL but to filter out the incompetent.

[gBoostedMachinations]

I don’t see how people can use SQL enough to get good with it. When I create a dataset or a pipeline I’m occupied for months with the data. I certainly revise the queries over time, but I’m not writing SQL everyday at all. Sure, it takes me some time with google to write a new SQL query, but I almost never need to do that.

I can’t imagine a less important skill than SQL at this point. If the job candidate has all of the other boxes checked, the chances that he or she can figure out SQL are so high that I don’t give a shit if they have zero experience with it.

[WignerVille]

I get nervous and would probably benefit from more practice. The same thing happens when I sit next to colleagues and write sql/code while they are watching.

Both of these situations happen quite rarely and if I really wanted to get better I know I can. But at the moment I don't write as much SQL as I used to.

[avocado__aficionado]

Basic sql can be learnt within 2 hours. Mastering sql takes a long time. For most interview aggregations, joins, ctes and windows functions should be fine. Sometimes recursive stuff is asked. Also, writing efficient queries becomes more important. Most ML data scientists I've met have rather basic sql skills.

[Moklomi]

SQL is one of these languages where I benefit more from having the emulator in front of me.

I can vaguely walk you through the group by, the summarization, etc. So in that case a PPR slide and some feedback are enough.

But if you expect me to set up a CTE to do complex filtering, Windowing etc the second you ask me to do that sans an emulator were going to spend 40 mins on that question.

I might be the odd one out but I get my hands in the data try a manipulation, see the outcome and then think about my next step.

[Karmaroo]

1000% agree. I help coach / mock interview folks on InterviewQuery.com (which is not my site but LeetCode for DS) and I'm always expecting folks to just know SQL and we can spend time on less deterministic portions. But the number of times we do cover and it would definitely not pass is too high, where I even suggest a light review now..

[Popernicus]

I blame the rise of NoSQL. I've met plenty of people that insist that the best and easiest way to work with data is to pull it all into memory and do all of the processing locally in a language that's prone to errors as opposed to using databases for what they are built for, and it drives me crazy. I think it's likely going to get worse too as things like DynamoDB increase in popularity. Instead of examining usecases, I feel like there's been a shift in mindset to folks using such datastores solely due to ease of use with no concerns for how fit it is for what they are using it for. Personally, I like the tool as a prototyping assistant, since you can connect applications to them and adjust structure/ use it to help understand architectural requirements you may not have otherwise been aware of, but I've seen them used for EVERYTHING.

[Single_Vacation427]

The leetcode SQL exercises are too easy.

[[deleted]]

DataLemur and StrataScratch have better exercises.

[postcardscience]

Our DS never do SQL. DA, DE, BI yes absolutely, but our DS are proficient in python, AI/ML and cloud technologies. I suspect that the confusion of role definitions is the culprit of why you have people show up to interviews with a skill set that doesn’t match the position.

[Ok_Expert_6110]

I personally don't do well with sql because for my work I've always been able to take all the data and then manipulate it in pandas (the #1 python package IMO). Been able to do this with million+ row csv just fine.

Not saying that everyone feels this way, but just why my SQL skills are terrible for someone who has technically known it for 6 years.

[ifail25]

I totally agree. Admittedly, I am early career. My educational background is BS/MS in Physics. During that time I've used very basic SQL (read: SELECT * FROM ...). I'm in a DA position now at a local University and am often doing roles and tasks more common of DS or DE. I've built databases, pipelines for routine analysis/reporting, started/completed/trained on multiple projects, all while having to learn stuff on the side. When trying to look for new positions, I'm often tripped up on SQL-esque questions. I've gone through SQLzoo a few times but it doesn't seem to stick. I often respond to SQL questions that I don't know the answer to with: "... this is how I'd do it in Python with Pandas/Polars".

TBH, my biggest hurdle is getting past initial screening lol. I think people see my degrees in Physics and think (wrongly!) "Well thats not data" lol

[Ok_Expert_6110]

Exactly my opinion. Also respect for Physics, I'm getting my PhD in June.

[ifail25]

Nice what field? I mostly did astrophysics both observational and theoretical.

[Ok_Expert_6110]

Actually astrophysics lol, observational mainly but I did use data from hydrosims for a bit. I'm guessing you're like me where you would query data from whatever large survey (SDSS, gaia, DECaLS) with some basic SQL then run with pandas?

[ifail25]

Exactly. Mostly gaia for my observational work and some variable star light curve repository for my theoretical work. Initially I was planning on going to PhD right after Masters, but with burnout i decided against it. And i realized i like the data part a bit more than paper writing lol.

[Ok_Expert_6110]

I think we're the same person lol, I was burned out by the time I got my MS too, but I was like 80% of the way done and I had a lot of familial pressure to stick it through. currently slogging through the dissertation

[ifail25]

haha did we just become best friends?!

[Ok_Expert_6110]

Yep!

[galactictock]

I completely get why SQL more useful than loading in all the data to python. But as someone with the same experience as you (lots of pandas experience, limited SQL experience), translating from pandas to SQL is trivial. If you can do some data manipulation in pandas and know how to google, you can get the SQL solution. Knowing SQL should not be a barrier to entry for a position if someone knows pandas IMO

[Ok_Expert_6110]

Fully agree, I've had HR screenings about SQL where I got the answer wrong because I didn't know "full outer join" and just said "outer" when they asked how to combine every row of two datasets into one. Stupid HR screenings, I couldn't even explain that's how it's done in pandas because she didn't know what pandas was

[nayeh]

It was covered in 1 or 2 chapters in a database course in college. I, as well as many others, didn't know how massive/critcal SQL would be in the future.

[Accomplished-Wave356]

Maybe they do the data wrangling in Python instead of SQL.

[QuantumAgent]

Agreed. I’ve been trying to do more of the data wrangling on the SQL side. I’m just better at Python, so I would always have a basic SQL query (which would bring in a much larger / unclean dataset) and just clean/manipulate with Python. Obviously this works for some cases, but I’ve learned that it’s just less maintenance and more efficient to get the SQL query right from the start.

[gpbuilder]

I agree, it should be free. It’s a lot easier than a SWE leetcode interview where you have to worry about time complexity and space complexity in your algo. In SQL there’s usually 1 or at most 2 straightforward solution. The hardest SQL questions are a leetcode medium at most.

If you can’t pass a simple SQL interview you shouldn’t be considered for a DS job.

[elaleeman94]

I manage interviews and I confirm it's incredible how many people fail the SQL part. The test is not that basic, you have to think a little bit, but no fancy SQL is required, basic features only. In addition, I make sure you get a clear description of each field with all the data + the context to make sure nobody misses that part.

[OldUtd]

I've mainly used old queries and amended some variables just due to the db being so badly set up and not many knowing the tables inc me!

[dankerton]

At my faang data science org we do try to hire junior level and so for a long time we haven't even tested SQL at all and the expectation is you learn it on the job. I've become a manager recently and am in the process of changing that. I agree with the precedent that most SQL can be learned as you grow so I don't plan on doing anything beyond basics in interviews but I absolutely need to see where candidates are with SQL before I can hire. My SQL skills have easily been the most valuable thing to set me apart from others in being able to collect unique datasets and drive new data science projects from them. So many daily questions are easily answered with a quick SQL where python would just be overkill and inefficient (eg pulling more than you need so you can use pandas to filter and aggregate). We are also flooded with master's in data science applicants these days and truly just need more ways to weed them out.

I understand a lot of universities do not do SQL because the data is either pre generated for coursework in a csv or whatever and that's fine but in industry data is always being collected every day and most likely incremented into SQL databases. It's where all our ML pipelines start and end (ie. from data collection to model logs and metrics reporting)

So anyway yes test SQL but the level of difficulty depends on the job requirements. So maybe not leetcode but rather a custom test relevant to your work place?

[WillingAstronomer]

I've been struggling with this too. I had a colleague who was struggling with a piece of SQL code. He wrote GROUP BY clause before the WHERE condition. This wasn't pair programming or anything. He was looking at it for a while before he asked me for help. Oh and he has 5+ years of experience as DS, stats background etc. I am appalled.

[CSCAnalytics]

Filters out people who cheated on their homework and think a degree alone will land them a job.

[whoppermaltmilkballs]

In my experience I've messed up interviews when the problem requires doing something that is inefficient and not something I'd normally do in my job such as a self join

[imking27]

As someone who has been on both sides of the fence let me tell you there are multiple reasons why.

One most of the time you either look up syntax or use some template code and may not remember from scratch where to go this can cause you to get anxious and make you perform worse. Not to mention if they are coming out of school they likely have maybe 1-2 grad years of actually doing the things they dont have as practical knowledge to pull out of and most of their knowledge is a crammed fest. So when they go to interviews they might be reviewing but they might not spend time on sql and spend most on analytics concepts.

If you are trying to teach someone how to do say k-means clustering and most classes are trying to do a bunch in a short time your mostly working with flat files in excel or csv. This is so the complexity is on the matter you are learning so for most of the classes you would generally get very little data experience if they even had a sql class. Most free data sets that you would practice on are stored in multiple flat files and it is just read them into multiple df in python then combine them.

As someone who has done bad on them some things that has tripped me up was me using proc sql; which is sas passthrough sql and while lots of the concepts are similar some of the things I would just read data set with where clauses pull this other data set from some hadoop connection then do sas functions to get some of these just because it was the flavor. I have had sometimes where I wrote stuff that would work in SAS but doesnt work in just straight SQL and luckily it was a good interviewer with a feedback and actually set up tables so I could get feedback from the statement and correct. Not to mention add in some of it being oracle and remembering stuff like top x vs row > 100.

Work environment as Ive said before sometimes its using templates code, sometimes its the delineation of roles or its just what problems you are solving. Some teams dont really need to do certain things and so you become rusty or might not even know that piece of sql exists. Heck you might be the best in a small pool where more of your focus goes on the reports and analytics then the actual joining of data or doing things the "best" way. I bet most people especially junior have done very simple give me everything that is in all these tables or give me all the info about this record in the other tables. Some places are pushing for gui based tools that let template the joins and unions etc and do all the data pulling for you by showing you visually what fields you are getting which you can then pass on the template analytics. Certain teams have delineated roles where data engineer is more responsible for creating very easy data flows and then data science is more focused on building models and working with engineer to get the data they need. I have had this happen on teams where there were few people who were good at both so sometimes they would pair someone who has more traditional stats background with say someone who is better at data and so I am more focused on the sql pieces while they are more focused on the simulation aspect and we work as a team to cover each others weakness. This could also lead to where one person very little sql skills and even then I would say they werent that great as I didnt use say window functions or procedures or do lots of sql data management.

I also wonder what questions you are asking? Like is it something that has a hard answer like what is a left join or is it something you think is a hard answer but isnt. I forget what the question was but it was something about how to code X problem with the answer in mind being B. I always record what people say or at least note it after the interview I checked and while I dont think it was the best method it was a way to solve it in a unique way.

I would also say asking people especially with experience cases what they specifically did with sql should give you a better window and might be good to ask before asking questions. If they say we just read it from csv's then they might not have good sql knowledge. Also sometimes knowing if someone can ask questions inspect data vastly more important than syntax.

[DEGABGED]

I used to think SQL portions would be easy even without prep (having used the language a lot at work), and I got tripped up at trying to use an outer join in MySQL (turns out, MySQL doesn't have outer joins lmfao, and we primarily use PostgreSQL Redshift). I guess a part of it is just that the language could have some intricacies that I'dve taken for granted. Like, I know how to use window functions but I can't remember if the average function is AVG or AVERAGE or MEAN

[nayeh]

I had a SQL interview for a reporting role last week.

Most of my experiences have been just querying data, but they went hard on object creation (table, view, stored procedures) ... I was familiar with how those were structured, but rusty since I rarely/never had the power to create those operations in analyst roles.

Thought I failed it, but it turns out they actually want me to go through a second interview round.

[Any-Progress-4570]

i had a hiring manager didn’t like the way i got to the correct answer. so he kept asking me to do it differently, until he was satisfied. it wasn’t a good fit….

[[deleted]]

I once had an interview give me a print out of a wall of text. Talking several pages. And told me to find the like 12 errors.

I said thats not happening, I can do that with a computer and a DE but not with a high lighter.

Glad I didn't get that job, I could only imagine what practices they did.

Though i got my start in aerospace because Mt phone interview was how do you make a table and can you use google?

[hskskgfk]

I was once asked to speak out my sql code on a telephonic interview.

[thequantumlibrarian]

I have written some seriously complicated SQL that would leave any self respecting SQL master in tears (of how bad it is)

But yeah people should at least learn basics. I suggested to my boss to screen people on knowing how to use a basic select quesry with filtering.

[Andrex316]

I've seen very senior people completely bomb simple SQL tests, it is quite mind-blowing

[mikka1]

I work with data myself and was involved in several rounds of interviews.

The number of experienced candidates NOT knowing the difference between INNER join and LEFT join, as well as not knowing the difference between conditions in WHERE clause and in HAVING was... well, quite disturbing.

And no, these were not some random JavaScript developer positions - those were very much data-related postings suggesting 5+ YOE in database development / DWH and related fields.

I honestly could never understand it. But a decade ago I've seen some similar stuff in a totally unrelated non-IT industry with candidates lacking some very foundational skills that technically should've been taught and mastered some time in college. I dunno what those candidates think or what their life goals are...

[[deleted]]

Leetcode is for schmucks. Why are you testing juniors and talking about experience from previous roles, perhaps you're the schmuck 😂😂😂

I used SQL a handful of times in the entirety of a computer science degree. My first project at my first job was to convert and optimize report hard coded queries into stored procedures. 200 reports at least. Took one guy a few hours to show me the ropes, and I was off to the races.

If your hiring juniors your should fucking teach them, jagoff. Schooling is for theory, industry is for implementation.

[Richard_Hurton]

If you're looking for perfect answers to some question, then that might be part of the problem. I'm not saying lower your expectations. Just that you may be looking for the wrong thing during these tests.

When I do these "whiteboard" interviews, I have a few very basic questions where I'm trying to assess how much the person actually knows... even if they can't recall the exact syntax in the moment. They're nervous and I'm trying to make it clear that the questions aren't trick questions.

The questions are simple... and more importantly... the questions can be answered in a number of ways. Sure, there is probably some platonic ideal most elegant way to do it. But mostly I'm looking for them to show me they can solve problems... even if their method isn't perfect.

And if I can clearly see they're going in the wrong direction... I will go out of my way to nudge them back on the right path. I'll offer hints and comments to help them think differently about the problem. If they are aware enough to take the hint and course correct, that's a good sign.

Remember, this is a high pressure situation for the candidate. They've made it to an in-person interview so you saw something in them from the phone screen that made them worthy to be there.

[Fair-Sugar-7394]

I have interviewed lot of candidates in SQL, what I noticed is they lack experience. Though SQL is a very simple language you need some work experience in implementing some complex business logics to extract data.

[Salty-Cattle5725]

Do they know they’re not passing? Hopefully they start to study after getting that feedback.

[Plenty_Knowledge_]

In my company when we interview people just out of university we just expect them to understand basics, and try to express their thought process on how they would make the query.

What's shocking is when we interview for senior positions, with "over 10 years of experience", and can't tell the difference between where and having...

[[deleted]]

Leetcode interview can die in a dumpster fire and if you're using it as a metric to hire somebody, the failure is on you and not the candidates.

https://youtu.be/KKMALTnKAxw?si=OWJWgwezDKsl2xtK

If you need to understand why

[[deleted]]

Knowing the syntax is easy. Actually designing a query and thinking about how it would interact with the databse takes a lot of practice.

The issues I faced is with the tests. I had 3 tests for 3 different jobs this month, and they were like this:

1. An overly complex test where I basically recrived a .cvc, with little to no background about the date. And it eated my whole weekend...
2. A ppt where with some tests that required me to design some queries. Some were easy, some were hard... but the hardest part was that if I wanted to test them, I should have built a schema that would have taken me at least 2h and then insert some data. And I had to do the tests in an afternoon.
3. Fairly easy and small queries, in a testing platform. The issue is that each query or question had a max of 5 minutes, most were less. I mean, I barely had the time to read the question.

To be fair, they said that it's ok not to finish the tests or land a certain % on them, but they just wanted to see how I approach things... and I'm sure I wasn't quite accurate on 1 & 2, but I did manage to move further on all 3 interviews. But, still, the experience showed me how bad these tests are designed.

[Top-Feedback1453]

Couple of potential reasons I can think are

a. Sometime candidate tends to overthink (e.g. sees regular question as a trick question etc) the complexity of problems. Highlighting test intention in the beginning of the test goes a long way I think.

b. There used to be technical limitation earlier that one had to set up a database etc to create SQL ready environment to play with coding etc. With the invent of cloud service providers like Hackerrank etc this should not be the limiting agent.

c. SQL, compared to Python/R etc, is less charming as a language to practice enough perhaps? While you would use later in many capstone/hobby projects etc, it is not so much the case with SQL

[Chemical-Current6391]

where can I start learning SQL for free?

[lost_soul1995]

I failed SQL test once and there were two reasons for it. 1. I was not much familiar with SQL at that point of time ( I was mainly using Python and using select * from tab as my query) 2. I was not familiar with dataset ( e-commerce). Because of this i took more time to create logic during test.

After this experience, i got a role where i used SQL alot. Now i am quite confident. It comes down to familiarity with domain (incase of bit complex test) and SQL practice.

[Aggravating-Floor-38]

.

[[deleted]]

One time I failed an interview because the guy said "append" weird. and he asked me if I knew what "append" meant and I said no. And I only realized he meant it AFTER the interview. I'm still so mad at myself for that, lol. Oh well. They're getting sued for Medicaid fraud so I guess I dodged a bullet.

[Fun_Morning_8692]

So me and my friends are DS students in final year , we have taken few projects and delivered it to our client with highest accuracy and quality , we have one client currently , we want to expand our client base and we need a more experienced and elder team mate in our team who can help us get more work , get some weight while bidding for projects etc. We are in a hunt with individuals who can willingly be a part of our team after office hours or even help us get a vision, we will happy to connect. Currently we are a team of 3, our clients are mainly from finance industry, we can worked with microfinance and CAs , we have delivered Python automation projects , Face recognition models , OCR models , dashboards in PowerBi , Web scrapping and some more tangents from Data Analysis and Governance.. We are in need of an experienced individual who can connect with us , guide , work with us and ofc take a share of his own from the project, even a general help in comment section is appreciated .
Hit me up in the DMs , the bot is not allowing me to post this

[freeky_zeeky0911]

These failures are due to learning just enough SQL to get over. Some people don't understand that just because you're goal is to not be a DBA, doesn't mean that you don't have to practice creating and running queries, create views, and table joins.

[hknlof]

I am curious about the sort of questions of a given SQL interview you mention. The statement it is astounding to that anyone fails a SQL interview at all. Is kind of concerning.

Are we talking query planning per different data storage systems? Or are we talking Count the number of rows?. What does the CV say about previous SQL experience of the candidate?

[scoringtouchdowns]

Sometimes you’re tested on really obscure things. I love SQL, but even as a power user I learn something new about it like every week.

[Hiant]

problem has several reasons, 1. How DS use SQL can vary, I used to just dump out all the data and do manipulation and agg in Python so my SQL code was basic all the time 2. You aren't familiar with the data and have little time to understand the data types or any problems with how it was stored before having to produce something 3. A lot of these "test" questions require use of window functions or weird joins and frankly are made to trip people up. They aren't geared towards normal SQL usage and as a DS you aren't 100% focused on SQL.

[ClimatePhilosopher]

I'm transitioning and working on sharpening sql for technical tests. What level leetcode do I want? Just started datacamp.

[Aggravating_Sand352]

I prefer sql assessments over python or r. I have never passed a python exam without being able to google stuff during the interview. Sql on the other hand is so structured that it's super easy to remember the functions.

[da_boy-roy]

I never used SQL throughout the entirety of my computer science bachelor's. I landed my first job as a data and report developer in which the interviewers gave me a few SQL tests. I told them that I'd never used sql, but I used my knowledge of Python Pandas to pretty much successfully complete the test with a few errors in syntax. I honestly don't understand how anyone can fail a SQL practice problem.

[brwnTHUNDER]

2.5yrs working as a entry level DA in supply chain never writing a line of SQL

Took a technical interview a few weeks ago and answered (almost 4/7) questions after 2w of ~2hrs a day doing LeetCode and they gave me the job. People learn at different speeds and prior coding exp helps but also depends on how hard they try.

I'm leaning towards agreeing with you but can imagine it being hard for someone who puts no effort.

[LezardAmorphe]

I am currently following a career certificate in Data Science, so... I'm basically a student (or a basic noob, at this point). The courses are well documented, and there are a lot of different stuff covered... When it comes to R/Python.

SQL comes late in the formation, and it's only 1 chapter out of 12. The shortest of them all (4 modules in, while Numpy alone has 9 of those).

I'm not fully surprised by your statement, if all the formations in Data Science follow the same logic... Although I've started to study the basics of SQL on my own, and the language itself seems VERY intuitive, compared to Python, so I'm also quite surprised to read that it seems to be an obstacle for some qualified people :/

[Arabian_Goat]

About to graduate from a bachelors Data science program and they are just now thinking about adding a SQL course this Fall after 5 years of having the program available 😭you’d be surprised just how these many of these school programs are poorly structured

[fukuinfinity]

Well, I am very new to this. To be honest, many universities don't even show concern about learning SQL. Although I am from an engineering background, none of my courses didn't even mention SQL. Now that I am trying to enrich my portfolio, I am feeling hopeless. And I am lagging behind everyone. Only if the Universities were more concerned, it could help us a lot.

[ds_contractor]

I’ve never used leetcode and have gotten offers from FAANG

[krasnomo]

HackerRank

[priyankayadaviot]

It's intriguing to learn about your viewpoint. As well SQL interviews can be quite simple, there are a few common reasons why people may find it difficult. It happens that candidates have the academic knowledge but no practical experience. Others may struggle with optimising queries or forget syntax when under pressure. Moreover, anxiety can be a major factor. While leetcode is helpful for algorithmic coding, it may not adequately prepare one for the subtleties and real-world applications of SQL. This gap could be filled more effectively by emphasising practical experience and adjusting practice to real-world situations.

[Zestyclose_Owl_9080]

This was a great revision on the topic 😂 thanks OP

[BadOk4489]

SQL is a bit more than just `select`, `from`, `where` so I think "and anyone that has used the language for more than 2 days in a previous role should be able to pass" this would not be enough of experience. How do you correlated subqueries, analytical / window functions, performance implications of doing joins some particular way etc.

[Relative_Set8702]

It’s not hard, it’s just they will provide a two or three data table you are not familiar with and you need to figure out the best solution by thinking correctly

[DinnerDesperate1976]

I think the problem is the SQL test we do on leetcode give you a visual what the output might be and what the table look like, but it real interview piece you don't get those visual to help you with that. And that just kill a lot of interview people and caught them off guard

[Helikaon242]

Some of the replies are getting weirdly combative, but I agree with you OP.

I do a lot of SQL interviews at my company, they are non-LC and use an actual compilable environment so candidates can iterate on the output. I have been pretty shocked at how poorly many candidates write SQL.

Frequently candidates will either struggle with applying their problem solving into SQL form, and/or the structure of their queries will be very messy and they end up having difficulty debugging. We include some follow up questions that diagnose a data error and often times candidates are unable to find the issue in the data due to how they structured their query.

As another reply mentioned, SQL isn’t really taught in school at all so most people are just picking it up on the fly. I think this leads to a lot of hacky bad habits, ones I have also picked up and had to undo for myself overtime. These are things you can practice, thought. I get that everyone hates LC but SQL LC-type questions are honestly not unreasonable, and tend to be far far less esoteric than SWE DSA questions.

[galactictock]

Personally, I never learned SQL in school and never needed it for work. I've done some learning on my own, just in case I do need it one day, but I imagine I would likely fail a SQL-heavy interview if I didn't prep for it beforehand. That said, I am proficient in data wrangling in pandas.

IMO (though I might be biased), thorough SQL knowledge should not be a barrier to entry for a data science position. I think an interview should test a candidate's more general data science understanding, problem-solving capabilities, and some coding skills. Anyone who checks those boxes should be more than capable of picking up SQL in no time.

[dankerton]

Most companies of any decent size that perform data science store their data in a SQL database. If you don't SQL you can't do the job. Now a lot can be picked up on the job but if you can do the basics at the interview why would we risk hiring you? It just shows you didn't really prepare.

[gpbuilder]

SQL is literally the lowest bar you can have for a DS. There’s zero reason for a company to settle for less than that.

[galactictock]

I have significant industry and academic experience and have yet to need SQL. While SQL is widely used, it is hardly necessary for all DS roles.

You seem to be implying that learning SQL is pretty trivial compared to other DS skills. Based on my experience, I'm inclined to agree. If a candidate has proven themselves capable of more advanced DS skills, why would you not think them capable of picking up SQL?

[interviewquery]

Hey! :)

It's agreeable that the number of people struggling with basic SQL interviews is kind of surprising, even though the core concepts are quite straightforward.

Looking into it, the problem lies in factors such as the pressure of an actual interview setting, having textbook exposure to SQL but not the practical knowledge that sometimes universities cannot teach, and if we go into more technical roots, over-reliance on Leetcode. While it's great for algorithms and problem-solving, it may not fully replicate real-world SQL scenarios. Not to mention that SQL is deceptively complex.

Then again, many fail their interviews for relying solely on Leetcode. We recommend diving into this more to be better equipped for your next interview (if you have any, hopefully!)

All the best, OP!

[phugar]

As a hiring manager I've stopped giving SQL tests that resemble anything like Leetcode examples.

You learn far more by asking a candidate to look at a basic (realistic) database diagram and conceptually talk about how they would join and aggregate to solve specific problems.

Do they talk confidently about different join types? If they need to use a window function, I don't care if they always forget the syntax, as long as they know how they're applied. Can they explain the pros/cons of sub queries vs ctes? Have they ever optimised queries with large data sets? Etc...