How to Practice SQL for a Technical Job Interview

You’ve scored yourself an interview for an SQL-related job. Nice work! But perhaps uncertainty is creeping in as your interview date looms closer.

• Do you know enough SQL to make the cut?
• What questions are you likely to be asked?
• What SQL practice should you be doing before your interview?

Almost all SQL job candidates go through exactly the same nerve-wracking process. Here at LearnSQL.com, we have the lowdown on all the SQL practice and preparation you’ll need to ace those interview questions and take your career to the next level.

People are choosing to learn SQL for a wide variety of reasons. There are many different types of SQL jobs (and database jobs) just crying out for your newfound skills. What they all have in common is the technical job interview. This can be intimidating if you’ve never encountered one before and aren’t sure what to expect.

Here are our top tips for preparing for an SQL interview!

Six Ways to Practice SQL Interview Questions

1. Practice SQL Queries

All theory and no practice makes Jack flunk his SQL job interview.

I’m not joking.

Knowing how to format an SQL statement in theory is all very well, but sometimes putting that book knowledge into practice is a whole other rodeo.

You might have read all the content we recommended in 50 Ultimate SQL Resources. You might think you’ve got it all figured out. But if you don’t challenge yourself with a few real-life SQL problems before walking into an interview, you could be setting yourself up for failure.

SQL test questions are a very specific animal. There’s a formula to these things, and you’ll never learn it without diving headfirst into real, hands-on SQL problem solving.

The good news is that there are a number of ways to get some job-winning SQL practice:

• Hop on over to the SQL Practice course on LearnSQL.com. This is the hands-down best place to review and consolidate your SQL skills before a big interview. The course is full of interactive SQL practice exercises that go from easier to challenging. The interactive code editor, data sets, and challenges will help you cement your knowledge.
• Once you’ve got that under your belt, spend some time studying the type of SQL questions employers are likely to ask in your interview. TestDome is a great place to do this. It offers a huge collection of SQL interview practice questions, which more than 5,000 companies actually use in their technical interviews. You’ll be thanking your lucky stars if a question you’ve studied on TestDome is in your interview!
• Another great place to get some SQL practice is w3resource.com. This site is jam-packed with exercises on everything from retrieving data to formatting query outputs and more. If you’re looking for a site for a few hours of dedicated SQL practice, this site should be high on your list.
• If you’re too tired to head all the way over to TestDome or w3resource, stick around and read LearnSQL’s very own picks for Common Entry Level SQL Developer Interview Questions. Tihomir has got you covered with answers to some of the most common SQL test questions, so you’ll feel well-prepared heading into your next technical interview!

2. Be Prepared for Anything

Knowing the very specific answers to some very specific SQL interview questions is great, but it’s not going to help you if you’re asked something unexpected. Don’t get me wrong – targeted preparation can certainly help. And there’s no better feeling in the world than acing a question you practiced. But if all you do is practice SQL interview questions while ignoring the basics, something is going to be missing.

Mastering SQL basics is paramount. If you feel you could use a brush up, look at LearnSQL’s comprehensive SQL from A to Z track. It will guide you through seven fully interactive courses that have everything you need to get up to speed with all the most important SQL topics.

What are the SQL basics, anyway? At the very least, you should understand:

• Basic queries – e.g. SELECT and its good friend the WHERE clause.
• Inner and outer joins – What’s the difference between them? When should you use each one?
• How to INSERT, UPDATE, and DELETE data – This is highly likely to crop up in a technical interview, so checking out the How to INSERT, UPDATE, and DELETE Data in SQL course is a smart way to make sure you’ve got these important commands down pat.
• ORDER BY, GROUP BY, HAVING – These three are fundamental to organizing data and are definitely something you will be tested on – if not in your interview, then very early on in your new SQL role!
• COUNT, SUM, AVERAGE, MAX, and MIN – These functions complement basic SQL commands and are vital when digging deep into data.
• Indexes – You need a good general knowledge of index types. And you’ll need to know when to use each one. This will go a long way toward a successful SQL technical interview.
• Transactions – How do you run, commit, or roll back transactions? Don’t get caught out by committing to an SQL query before it’s ready.
• Window functions, recursive queries, and SQL reporting – Depending on the job role and experience level, you may want to review your knowledge of these three SQL techniques. LearnSQL offers "Window Functions" course and "Recursive Queries" course if you’re looking for help.
• Triggers – Understand when and how stored procedures are automatically invoked by a predefined event.

3. Know Your SQL Lingo

Image: XKCD

If you don’t understand this joke, you’re not ready for your SQL interview.

It’s not that your potential employers are looking for someone with a dry wit. But they are going to be looking for a candidate who knows what they’re talking about.

If they mention RDBMS or recursive queries and your eyes glaze over, then you’ve got a problem.

Knowing the lingo means knowing your field. Language is the very heart of SQL, so if you’re unsure what some of the concepts mean or if you can’t explain an acronym or two, your interviewers are likely to write you off as a rookie. A rookie you may well be, but you want to come off as a knowledgeable rookie.

If you’re interviewing for SQL-related jobs, you shouldn’t have to think about what a ‘client’ or ‘primary key’ is – both should now be part of your vocabulary.

What exactly do you need to know? We won’t pretend the list below is exhaustive; there’s no such thing. But you shouldn’t put on your best business shirt and a winning smile without knowing the following terms:

• Database Management System – A software system that facilitates the organization of data into a specific database architecture. The most popular DBMSs include MySQL, Microsoft SQL Server, and Oracle.
• Server – A program that services the commands that come from client applications. An SQL server does not have a user interface – you need to use a client to talk to the server.
• Aggregate query – A query that summarizes information from multiple table rows by using an aggregate function (such as SUM or AVG).
• Client – An application that makes requests to the server.
• DDL – Data Definition Language (DDL) helps define data structures. It uses commands like CREATE, DROP, RENAME, and ALTER.
• DML – Data Manipulation Language (DML) is what we use to work with and alter data. It uses commands like MERGE, INSERT, and UPDATE.
• Query/Statement – They’re often used interchangeably, but there’s a slight difference. A statement speaks to the database. A query asks something from the database.
• Predicates – These narrow down the results of an SQL query. A few examples are =, <>, IN, BETWEEN, LIKE, and IS.
• Stored procedure – A set of SQL statements stored in a database and executed together.
• Primary key – One or more fields in a database table with values guaranteed to be unique for each record.
• Foreign key – A column that identifies records in one table by matching with the primary key in a different table.
• Normalization – The process of organizing data to minimize redundancy.
• Record – A set of values in a database table, shown as a row.
• Transaction – A collection of database operations treated as a unit. Using a transaction ensures that if something goes wrong, changes that were made before the point of error will not impact the database. Transactions typically start with a BEGIN command and end with either COMMIT or ROLLBACK.

Finally, please know what SQL stands for! (Hint: It’s Structured Query Language.)

via Gfycat

4. Understand SQL’s Place in the World

Being an SQL whiz on a technical level is important. If you also understand the role of data science in business, you’ll be at the top of the list of job candidates. What makes you truly valuable as a data scientist or database administrator is understanding the why behind the queries you’re writing.

• Why does the company need SQL?
• Why is data important to the company’s key performance indicators?
• Why does the company want me to ask these particular questions of the data?

Those in the data science field can often face the problem of failing to see the forest for the trees. Up to 85% (according to Gartner) of data science projects fail because they didn’t have the right strategy. If you’re part of the technical team, that’s not exactly your problem – but if you have a head for planning, strategy, and database design, you’ll be snapped up for SQL jobs faster than you can type COMMIT.

Want to get a better idea of your place in the big wide data science world? I highly recommend listening to some podcasts on the topic. Data Crunch, O’Reilly Data Show, SuperDataScience, Data Stories, and Analytics on Fire will open your eyes to the strategy behind data projects and help you better prepare to wow your future employers.

5. Be Honest About Your SQL Skills

On the topic of knowing your stuff, here’s the best snippet of advice: BE HONEST.

There’s not much to this. It’s one thing to be starting out, to have little experience and a lot of struggle to get your foot in the door of a new job, but over-stating your SQL skills? That will get you nowhere fast.

If lying about your SQL experience doesn’t get you at the interview stage, it sure as heck will come back to bite you when you’re sitting at your new desk wondering which buttons to push (and, equally terrifying, which ones not to push).

Don’t forget that interviewers aren’t just looking for an SQL wizard. They also want an all-round decent human being. Be humble. Be honest!

6. Get Some Real-World SQL Experience

Last but not least, one of the best ways you can prepare for an SQL interview is to go out into the world and get some real, money-in-your-pocket SQL work experience.

There are a number of ways to do this.

If you have contacts who work with SQL, ask if there’s a project you can help with – a bit of good old-fashioned work experience.

If you don’t have someone you can approach, try freelancing on gig sites like Guru, Upwork, and HackerRank. You may feel wholly unprepared for taking on a real-life SQL challenge. But I think throwing yourself in the deep end is not only the best way to learn, it also gives you fantastic experience to reference in your interview.

If you get a gig troubleshooting some database issues for a small bank in Bhutan (why not?), then you can now legitimately say that you’ve contracted your SQL skills to the banking sector. Success!

SQL Practice Makes SQL Perfect

Interviews can be intimidating. I don’t know a single person who actually enjoys them, but they’re interviews are a necessary evil for job hunters. As with most things in life, preparation is key. Getting a good amount of SQL practice before your job interview can certainly put you ahead of your competition.

Bear in mind the advice we’ve outlined here. It’s not about memorizing the answers to SQL practice questions. If you don’t also have an excellent grasp of SQL basics and a good understanding of why the company needs SQL to achieve its goals, you’re not covering all the bases.

Add to those things a healthy dose of honesty about your skill level, a bit of real-world practice where possible, and some seriously impressive fluency when it comes to SQL terms and concepts, and you’ll be ready to knock that job interview right out of the park.

And if you haven’t actually landed a job interview yet – don’t fret! Check out these Top 10 Websites That Will Help You Find The Perfect SQL Job!

Good luck!