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Category: Learning

Thoughts on Technical Interview Questions

Published 2022-05-10 by Kevin Feasel

Steve Jones shares some thoughts:

Redgate had a discussion recently among our developers about our interview process and questions. There has been a standard question asking candidates about 2D arrays, but as one developer pointed out, we don’t use these in our code base. So, why do we ask candidates about this topic?

The developers came up with a different question, actually a series of questions that ask about a class and then how to test parts of this class. We mostly work in C# in a DevOps culture, so this seemed like a good idea. They proposed a scenario with a few questions and then asked current developers to solve the questions and give feedback on the language, structure, and difficulty of the problem.

Read on for Steve’s thoughts. It’s been a minute since I’ve given an interview (a plus side to having a really stable pair of database teams the past couple of years) but one of the things I enjoy doing is taking screenshots of Management Studio in various phases of work and ask “What do you see here? There are no right or wrong answers.” I say the latter because I don’t want you to enumerate through every string you see on the screen; I want you to explain what information of importance you’ve caught.

One big tip for interviewers: instead of algorithmic or gotcha questions, show actual code at the 25th, 50th, 75th, and 95th percentiles of difficulty within your code base, focusing on things a person could understand with about 20-30 lines of code and zero context. “Difficulty” can mean that this code was tough to write, is tough to maintain, or that you have included common (and sometimes uncommon) errors to an otherwise real segment of code. For database developers, that might include things like invalid NULL checks, incorrect assignments, etc. Ask the person to perform a code review and point out what they see that is interesting. That way, you get an opportunity to check their technical bona fides in a realistic but relatively low-pressure scenario by simulating the activities that a person actually would do in the job.

I have more advice but I’ll save that for another day.

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Debugging a Production Failure

Published 2022-04-25 by Kevin Feasel

Roel Hogervorst diagnoses trouble:

When you are in panic mode you focus on what is right in front of you and make suboptimal decisions. Here is some I have made.

Read on for a couple stories as well as a practical implementation of debugging as an OODA loop. Something that Sean McCown mentioned before has always stuck with me: it’s amazing just how few people know how to troubleshoot issues. Our inclination seems to be one of two things: adduce a conclusion from the first piece of evidence (usually just a flimsy error message) or immediately give up.

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Animated SQL: Visualizing Query Operations

Published 2022-04-19 by Kevin Feasel

Steve Jones looks at an interesting site:

While I think SQL is interesting, I know some people struggle with the way the language work. Someone at work posted a link to this site: https://animatesql.com/

I think the idea is this site helps you visualize how a SQL query works. It’s not free form, and I can’t just write any SQL, but you choose a keyword and then a sample query is shown. If you press Visualize, it walks through how this query is processed.

Click through to see how it works and Steve’s thoughts. It looks like they’re using either MySQL or Postgres in the background; it’s hard to tell because both support all of the site functionality including LIMIT/OFFSET (versus TOP and OFFSET/FETCH). Sadly, it’s pretty limited in terms of the queries supported—for example, I tried adding in a quick ROW_NUMBER() window function and that did not go over well. Still, I like this a lot as a teaching tool, especially for people brand new to SQL and haven’t sorted out how to think in sets.

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T-SQL Advice for Beginners

Published 2022-04-19 by Kevin Feasel

Rob Farley offers some advice:

Following on from my last post… what advice would I give about T-SQL to my younger-self?

Well, for that I’m going back a long way. To when I had learned about queries, but still had some way to go.

It’s the same advice I give to everyone who’s learning to write T-SQL, even the most basic of beginners. And that is to understand that the queries you write get turned into execution plans, and it’s them that actually run.

Read on for some good advice.

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Index Design Guide Updates

Published 2022-02-24 by Kevin Feasel

Kendra Little has a guide for us:

We’ve recently updated the SQL Server and Azure SQL index architecture and design guide. This article is an in-depth guide to indexing in databases using the SQL Server engine, including SQL Server, Azure SQL Database, Azure SQL Managed Instance, and Azure Synapse Analytics.

Our recent update adds a table to categorize the types of indexes discussed in the article, clarifies B-trees vs B+ trees, and describes how row locators (aka “secret columns”) are used in nonclustered indexes.

Read on for more information and do check out the guide.

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Preconceived Notions: “Databases Are Easy”

Published 2022-01-11 by Kevin Feasel

Rob Farley takes us back to school:

At university I studied Computer Science, which felt like it was mostly about algorithms and paradigms. It covered how to approach particular kinds of problems, what languages suited what problems and why, and how to model things. The answer to a lot of things was “C’, whether it was a multiple choice question, or the question about which language would be used to solve something.

I skipped the database subject. Everyone said it was overly basic, easy marks, and not particularly interesting. I wasn’t interested in it. Not when there were subjects like Machine Learning where we’d implement genetic algorithms in LISP to find ways to battle other algorithms in solving the prisoner’s dilemma. Or the subject where we’d create creatures (in software) that would follow each other in a flocking motion around a cityscape. Everything I heard about databases was that they were largely of no importance.

In fairness, university database classes tend to fall into one of two categories: either mathematical forays into set theory or fluffy, school-of-business-friendly “Today we’re going to learn how to write the word SELECT. Next time, we’ll learn how to write the word FROM” types of courses, at least from what I’ve experienced.

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Lessons Learned Troubleshooting High CPU in Azure SQL DB

Published 2022-01-07 by Kevin Feasel

Kendra Little has an after-action report:

I’ve just had the pleasure of publishing my first new article in the Microsoft Docs, Diagnose and troubleshoot high CPU on Azure SQL Database.

This article isn’t really “mine” – anyone in the community can create a Pull Request to suggest changes, or others at Microsoft may take it in a different direction. But I got to handle the outlining, drafting, and incorporation of suggested changes for the initial publication.

It was a ton of fun, and I learned a lot about Azure SQL Database in the process.

Click through for what Kendra learned specific to Azure SQL Database, and also read the article itself.

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