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Our SQL interview questions

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Re: Our SQL interview questions

#141

Post by j-kidd »

jacques_chester wrote: post #8
free wrote: post #3

They seem to be quite simple. For what profiles are you asking these questions?. I have used very similar questions for dev ops role.

They're good questions because they go past the two simplest query types: select from ... where ...; and select from ... join ... where; Those are the types 99% of programmers who use SQL for simple CRUD apps know. But they come up short for asking more useful business questions. Eyeballing the list, it tests subqueries, GROUP BY, HAVING, OUTER JOIN, IN/NOT IN and SUM. Fairly useful primitives for general query writi…

For interview question, the keyword I like best would be EXISTS. Sadly, many developers write SQL for years without knowing its existence. If I am not mistaken, the propel ORM of symfony doesn't even have native support for it.

As shown by codegeek, the 6 questions here can be answered without needing sub-query. Maybe we can add something like "List employees who are not working alone in their department"

Re: Our SQL interview questions

#142

Post by twistedpair »

jebblue wrote: post #90
oneandoneis2 wrote: post #37

Earlier quoted context omitted.

You've heard of the FizzBuzz test, right?

I heard about it in the last year or so here on HN, otherwise I wouldn't have known what a FizzBuzz was. I've been coding for 20 years professionally and 30 for fun. I've never coded a Fibonacci either. I think colleges need to teach how to code a microcontroller to do something, build a multi-platform application, build a database application, set up a CI server, etc.

Fibonacci? That's a recent invention, right?

Re: Our SQL interview questions

#143

Post by pessimizer »

xanadohnt wrote: post #84

If the position you're filling is directly dependent on more-than-average SQL experience - creating a DB driver, an ORM, for ex. - then SQL-specific questions are applicable. But, by and large, this type of specific-knowledge testing is not very useful. I want to see a developer's general abilities at problem solving and the source code to back it up. If you have solved complex problems in C# - and can prove it - the…

These are very simple, though. If you say that you know SQL (or have known SQL, but are a bit rusty) and you can't at least make a strong showing on these questions, you are lying.

This is not complex problem solving, this is problem solving. I'm not sure what memorization has to do with any of this. SQL is a language with only maybe 10-15 important words. It's not like trying to get around Paris without a phrasebook as a non-French speaker.

I've found that using graphical query writers (I only know of the one in access) and ORMs are generally harder than writing the SQL. ORMs are good for keeping code db agnostic, though.

Re: Our SQL interview questions

#145

Post by pessimizer »

LekkoscPiwa wrote: post #25
jacques_chester wrote: post #22

Earlier quoted context omitted.

These aren't "details memorised from a manual". These are fundamental primitives of SQL queries. You simply cannot express most serious questions without them. If someone came to me and I asked them to write fizzbuzz, an answer of the form "I would google if-thens and modulo and print statements" would be a pretty obvious no-hire.

I would imagine questions that are good to start with: how you as a developer usually start a design of a database? How do you plan it? I got this question once, I thought it was really good. On the spot I could tell the engineer who asked me that is experienced. Can't answer that after reading sql book two days earlier. In contrast to the questions from the post.

What if you're not looking for an experienced data modeller, but someone who can write SQL?

Also: If you can read the SQL book two days earlier and answer these questions in a reasonable amount of time - sounds like an insta-hire to me. There's certainly nothing so hard about SQL that you couldn't do that - but some people who spend a lot of time working with databases seem to find the climb insurmountable.

Re: Our SQL interview questions

#146

Post by brixon »

jasonkester wrote: post #6
brixon wrote: post #2

My first weed out question is asking them to describe a Left Outer Join. They don't have to get it exactly right, I just want to see if they ever did anything more than a two table inner join. For a Web Developer the first weed out question is to tell me the difference between a GET and an POST. Here all I really want then to know is that a GET is what generally see in the URL and a POST is commonly what you see in H…

Careful using that terminology. You'll get false negatives on people who still think in terms of *= syntax, and will tell you that the words "left", "outer", and "join" are all redundant and probably don't belong in SQL in the first place. I used to be one of those guys, but I'm much less grumpy about it these days so I'd still pass your test. I have a sad suspicion that I'm on the progressive end of the spectrum whe…

True, I use it for a conversation starter. You can tell the split second after you ask the question if you will get any kind of reasonable answer.

I personally have used the *= syntax more than the LEFT syntax, but that concept has helped filter people since I am not allowed to "test" people.

Re: Our SQL interview questions

#148

Post by btilly »

The question List all departments along with the number of people there has an answer using a correlated subquery, rather than a join.

I have a relevant story about that.

About 9 years ago now, another developer escalated a bug to me. Every time they ran a complicated auto-generated query, they got logged out of Oracle. No way! I tried it. Happened to me. Began trying to narrow it down. Ran out of connections. Got a DBA to unwedge the machine. Began again. Ran out of connections again. Got the same DBA to unwedge the machine. Received a lecture about not opening so many connections, replied that I was tracking down a bug and had no choice. Showed him the bug. He was astounded.

Not long after I finished tracking it down and sent them the fix. Showed it to the DBA who verified that it had been reported already, and was fixed in the next release.

The bug was that any time there was a correlated subquery with no records, Oracle logged you out. My guess is that something, somewhere, followed a null pointer. The obvious solution was to move to a left join. If I remember correctly, the way it was being autogenerated made that hard. My solution was to have a correlated subquery which was a left join on DUAL so that there was always a record.

Re: Our SQL interview questions

#149

Post by ceejayoz »

jbverschoor wrote: post #30
LekkoscPiwa wrote: post #21

I'm not a SQL Developer, but anytime I get questions for which Google has answers to be found in 5 minutes or less, I'm quite hesitant to work there. I respect interviews that go along the lines of: "What would you do if..." after giving a detailed description of their environment. But then again I'm a tools/OSes admin, so maybe it makes more sense for my job description. But anytime guys are too focused on third opt…

I don't run a school. Anytime a web-developer does not know basic sql or other basic knowledge, I refuse to pay salary, and even deduct the 1$ per minute. That five minutes just cost you $10

I'd guess that's a labor law violation in most developed nations.

Re: Our SQL interview questions

#150

Post by VLM »

chrislomax wrote: post #130
VLM wrote: post #116

Earlier quoted context omitted.

"Wow. Is this the state of our industry now?" Traditionally this happens when HR demands "10 years experience with windows server 2007" and you somehow snuck thru (or maybe worked at MS on the dev team, or were in a beta program or...) anyway by definition the only people making it thru the filter are going to have a weird/cool/interesting background or are going to be pathological liars who inevitably will only get…

Without seeing any real data, wouldn't that all be a WHERE clause? I wouldn't imagine the skill was an aggregate of the applicants. I've just skimmed over this though, I'm not having a go

Ah I was trying to imply two sets of filtering and probably have them reversed, where HR is filtering on lack of honesty which only implies lack of skill or at least average skill, whereas the secondary filtration (the having clause) would imply the test for skill.
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