Top SQL Interview Questions You Should Be Prepared For In 2020

Written By Connie Benton

SQL interview questionsAs a programmer on the path to becoming an SQL developer, you’ve been working hard to learn data management. But even if you’re confident you can create and configure databases, there’s one crucial thing that stands between you and the job of your dreams: the interview.

Interviews make a lot of novice programmers anxious, and rightfully so. When you spend so much time practicing tech skills, building confidence doesn’t seem to be a priority. However, when it comes to the interview, a confident programmer will look more competent, regardless of their actual experience.

Lucky for you, there’s a sure way to build up your confidence before an interview: learning what type of questions you’ll have to answer during an interview. Do this, and not only will you come prepared, but you’ll be way more likely to land your dream job.

Let’s take a look at possible questions you might face, and so make sure you’ll be better prepared than the competition.

Basic SQL Questions

The first couple of questions you’ll get will be about your education and previous work experience, and they will be pretty basic. These questions will cover your understanding of basic SQL features and functions.

One of the most popular questions is: What are the sublanguages of SQL? 

The interviewer may ask you to list them or to explain the difference between, say, DDL and TCL.

You may also get questions about the data types. For instance: What is the difference between binary and varbinary data, and where would you use either? 

Providing examples for blobs and clobs may also appear on the list.

Be prepared to explain some basic functions of SQL as well. You may have to specify what sublanguage a function belongs to. Listing types of JOIN and explaining the proper usage would be something you should see in the first part of the interview.

You may also hear a question about data manipulation. That would be listing normal forms of data, explaining what index is, or how triggers work.

Most of these questions are easy to answer, even for a novice. If you know your SQL well, you would not be stalled by these. If you’re still feeling uneasy about the basics, read up on SQL well before the interview.

Jonathan Gennick’s SQL Pocket Guide would be the best place to look. If you want a more in-depth book, check out Robin Nixon’s Learning PHP, MySQL & JavaScript.

Database Management Systems (DBMSs)Questions

What comes next are usually questions about DBMSs. In most cases, that would be MySQL, as it’s one of the most popular systems. However, you need to be ready to answer basic questions about PostgreSQL and Oracle as well, just to be sure.

If you know that the company you’re interviewing at uses only one DBMS, at least know the difference between that system and other popular ones. Knowing the answer to why would you rather use MySQL instead of PostgreSQL for read-heavy applications may not be necessary if the company is mainly using MySQL but shows your level of understanding.

Also, be prepared to talk about the basic features of DBMSs like types of tables and limitations.

Since offices are now massively migrating to remote work due to the 2020 pandemic, you may expect a simple question like how do you access a MySQL database while using a VPN on iOS or any other OS. After all, endpoint security is important.

Code Execution Tests

You can read the books and manuals all you want, but ultimately, you can’t master SQL if you can’t read and write code. This is what the interviewer will be testing after you’ve gone through the basics.

The first type of question would be a task to read a piece of code. You’ll get a line or a couple of lines of code, and you need to say what the code executes.

Also, the interviewer may give you a table, or code that creates a table, and a line of code. Based on both of these, you’ll need to say what the code will return.

After you show you understand code, it’s time to write your own. You may start with explanatory questions like how do you avoid duplicate entries or how do you merge two tables with no overlapping rows. Explain how you would do that, and you’re off to the next step.

The next step is actually writing code. You may need to write a piece of code to execute what you’ve been talking about or write something completely different.

Often, you will have to create a table first and manipulate data in it to show you know more than one SQL sublanguage. Sometimes, the interviewer will ask you to write that code without using the most straightforward command to see how inventive you are.

Don’t quite understand what you need to write? Ask the interviewer! 

As weird as it may sound to a beginner programmer, asking questions and clarifying your task is actually a very important skill for a programmer.

If you ask nothing and end up writing something that doesn’t work or doesn’t satisfy the interview question, you show that you don’t have any soft skills, and you more than likely won’t land the job.

Database Design Questions

Database questionsEven if you’re applying for a junior SQL developer position and will be writing pretty simple code as a part of your job, you need to understand the bigger picture. The interviewer will probably ask you a couple of questions about database design.

As with SQL questions, these will start out pretty simple—like having to explain what is a factless fact or to illustrate the difference between OLTP and OLAP.

Then, you’ll probably have to look at some database schemas and comment on how they interact. The best way to learn how to do that is to look at tons of schemas. You can do it online at or pick up a copy of Beginning Database Design by Clare Churcher.

Be Flexible, Get the Job

The bottom line is, you can expect certain types of questions, but you can’t know the exact questions you’re going to answer at an interview. Any decent company would have their own system of interviewing in place and their own questions made by senior employees.

What you can do is prepare yourself for the interview and clarify what you need to do in the hardest parts of the interview. This won’t look unprofessional; you’ll only show your soft skills.

Make sure you don’t keep asking too much, though, as most interviews are limited to 45 minutes. If you’re stuck, however, you’ll always be able to buy yourself some time during the interview. You can buy a couple of seconds by clarifying the question and save yourself the embarrassment of sitting in silence when thinking about solving a problem by thinking out loud.