Tell me you've heard this interview question before. It seems like most candidates now know how to explain the differences between an inner and outer join by detailing the shape and shading of everyone's favorite Venn diagram.

Just last month I asked a candidate this question and they answered it perfectly, only to fail miserably when I asked them a simple question that actually needed use of a left join. But that's the thing about concepts, they can be easily memorized but also easily forgotten when not practically applied in repetition.

This week I wrote a blog post on the three SQL concepts every data scientist needs to know with example questions and solutions on how to solve them. I honestly think they encapsulate about 80% of all of the SQL interview questions out there because I use these concepts 80% of the time I write queries.

Relevancy in interview questions is also tough when it comes to working on and finding technical SQL questions. Half of the time in interviews you're wondering why the interviewer is asking you if mysql specifically uses DATE_ADD vs DATEADD. And the other half of the time the interviewer is actually asking about solving a thoughtful practical data analytics problem in SQL they might encounter every day.

Interviews suck! But they generally suck less when you've seen them all. And while I can't say that every interview you get won't be terribly condescending and irrelevant, I can preach that it takes real dedicated practice of interview questions, coming up with a solution without looking at the answer, and then checking your work to improve on getting better at interviews every day.