Developer Interview Questions

Front 1

Explain why DBAs don’t like cursors.

Back 1

I like to phrase this interview question this way because I’m not saying the DBA is right – I’m just asking the developer to explain the DBA’s point of view. I don’t have a problem with the developer rolling their eyes as they explain the answer, but I have a problem with the developer being surprised by the question.

The candidate gets bonus points if they seem even vaguely aware of the terms “set-based processing” and “row-based processing”, but that’s purely a bonus. (I wish I could say that these concepts are requirements, but in today’s economic market, companies don’t always want to pay top dollar to get the best candidates.)

Front 2

Where do you like business logic – in the app or in the database? Why?

Back 2

Personally, I like stored procedures because they’re easier for us DBAs to test, tune and tweak. On the other hand, the developer community isn’t always as fond of stored procs.

Front 3

Explain when and how transactions should be used.

Back 3

Start with just that open-ended interview question, and if they have trouble getting started, give them a scenario.

Front 4

Explain referential integrity and where it can be enforced

Back 4

What’s an orphan? How do we make sure that we don’t end up with OrderDetails for records with no matching Order record? Where are all the places we could enforce referential integrity? (Think foreign keys, triggers, the application, or not at all.) Have you worked in places where there was no referential integrity, and what problems did you run into?

Front 5

What’s the fastest way to get a thousand records into the database?

Back 5

I’m not looking for the best answers – I’m just looking to hear that they’ve done some work to performance tune their queries. If they’re doing fully logged individual record inserts, one at a time, into a data warehouse-size system, we’re going to have problems down the road. (Yes, I’ve actually worked with a BI developer that did millions of individual inserts per night in full recovery mode and thought the performance was the database’s fault.)

Bonus points if they link back to the previous interview question and talk about whether or not they should disable constraints or referential integrity during data loads. (I don’t care what their final answer is, but I just want them to know the pros and cons.)

Front 6

What’s the difference between a primary key and a clustered index?

Back 6

This is almost a bonus question. Most of the time, the candidate doesn’t know because it’s a function of the data modeler or architect, not the developer. However, I want to see how the candidate reacts to tough questions. Ideally, they say in a relaxed tone of voice, “I’m not sure, but I know who I’d ask.” If they don’t mention where they’d go, ask them where they go for SQL Server answers. Speaking of which…

Front 7

How can you tell if a query will scale for production?

Back 7

I want to hear that they do things like load tests or maybe look at execution plans.

I’m sometimes comfortable when a senior developer says things like, “I can pretty well tell when something isn’t going to scale, because I know the production boxes really well.” The key is asking a followup question about times when things didn’t scale.

Front 8

When is the DBA right?

Back 8

Always, kid. Always.

Front 9

Imagine I've logged you on to a machine here and brought up a terminal. You type wget http://www.google.com/. What happens?

Back 9

, with my networking bias, answered starting with the DNS resolution, moving on to proxy configuration, and then on to the routing decision and establishment of a TCP connection; another candidate answered in terms of the HTTP conversation. When I asked the interviewer what the best answer he'd heard was, his response was:

"Well, it started with the keyboard interrupt..."

Front 10

Do you use source control?

Back 10

y

Front 11

Can you make a build in one step?

Back 11

n

Front 12

Do you make daily builds?

Back 12

y

Front 13

Do you have a bug database?

Back 13

n

Front 14

Do you fix bugs before writing new code?

Back 14

n

Front 15

Do you have testers?

Back 15

n

Front 16

Do new candidates write code during their interview?

Back 16

y

Front 17

Do you do hallway usability testing?

Back 17

n

Front 18

hallway usability test

Back 18

allway usability test is where you grab the next person that passes by in the hallway and force them to try to use the code you just wrote. If you do this to five people, you will learn 95% of what there is to learn about usability problems in your code.