12 SQL Interview Questions and Answers

How do we answer complex questions, establish baselines, create benchmarks, and make informed decisions? Simply put—it’s data. When you learn how to answer commonly asked SQL interview questions, you could land a high-paying database administration job monitoring, retrieving, organizing, and managing this data.

There’s always a need for database administrators and architects. In fact, the Bureau of Labor Statistics projects a 9% increase in new jobs in database administration over the next 10 years. Once you’ve completed your SQL developer or database administrator resume, turn your focus towards making a great first impression during your job interview.

Below, you’ll find 12 interview questions on SQL and possible ways you can answer them.

12 SQL Interview Questions and Answers

1. What Is a Database and What Are Its Primary Functions?
2. What Is SQL and How Is It Used?
3. Explain the Difference Between SQL and MySQL.
4. What Are Constraints in SQL?
5. Which Subsets Exist in SQL and What Do They Do?
6. Describe Both DBMS and RDBMS and How They Differ.
7. What Are Tables and Fields in a Database?
8. Describe the Difference Between DELETE and TRUNCATE Statements.
9. What Is a CASE Statement and Why Is It Used?
10. What Are Keys in SQL and How Are They Used?
11. How Proficient Are You in SQL Server?
12. Describe an SQL Query Process.

Question #1: What Is a Database and What Are Its Primary Functions?

This is one of the most basic SQL interview questions employers will ask to gauge your knowledge of database purposes and functions. When creating your answer, be sure to focus on the following details:

• The definition of a database.
• Why databases are used.
• Types of databases.

How You Could Answer

“A database is an organized collection of data that’s easily stored, shared, accessed, and retrieved. The primary function of a database is to store and organize large amounts of data used for businesses, financial transactions, government agencies, products, services, and much more. Organizations use the information stored in databases to make informed decisions. There are generally four types of databases: document databases, graph databases, column-oriented databases, and key-value stores.”

Question #2: What Is SQL and How Is It Used?

Now that you’ve discussed your knowledge of databases, you’ll need to demonstrate your understanding of SQL. Your answer to this question should cover the following areas:

• The definition of SQL.
• Its functions.
• Why SQL is used.

How You Could Answer

“SQL is short for Structured Query Language. It’s a programming language used to update, insert, access, delete, and retrieve data. SQL is also useful for creating reports and queries for analysis and data mining. SQL is the standard programming language used for communicating with and managing databases.”

Question #3: Explain the Difference Between SQL and MySQL.

It’s inevitable that you’ll also encounter MySQL interview questions during your interview. To demonstrate that you understand how MySQL works, you should be able to compare it to SQL.

There are three components you should include when answering SQL interview questions that ask you to differentiate between SQL and MySQL. These include:

• A definition of both SQL and MySQL.
• Key functions of SQL and MySQL.
• An example of why they’re different.

How You Could Answer

“SQL is a programming language that runs queries and manages database systems. MySQL is an open-source relational database management system—also called an RDBMS—which was developed by Oracle. It’s one of the most popular database management systems on the market. MySQL uses SQL to manage data stored in databases and servers. For example, MySQL is often used to allow clients to access data while building or managing a website.”

Question #4: What Are Constraints in SQL?

Once you’ve gotten past the basic SQL interview questions, a hiring manager will ask you to delve into the technical aspects. An understanding of database constraints is key to successfully landing an SQL developer or data analyst job. Include the following details when creating your answer:

• What constraints are and what they do.
• Types of constraints.
• An example of how constraints work.

How You Could Answer

“Constraints limit the type and amount of data that can go into a table. There are seven constraints in SQL, including NOT NULL, DEFAULT, UNIQUE, CHECK, PRIMARY KEY, FOREIGN KEY, and INDEX. These constraints ensure the accuracy and consistency of data in tables by specifying certain rules. For example, a NOT NULL constraint prevents columns from containing NULL values, whereas UNIQUE constraints ensure that all values are different.”

Question #5: Which Subsets Exist in SQL and What Do They Do?

SQL subsets are commands designed to allow users and administrators to manage or alter databases. When interviewing for a job where you’ll use SQL, a hiring manager will likely ask you to identify the key subsets in databases and describe how they work.

Here’s what you should include in your answer:

• The types of subsets.
• The function of each subset.

How You Could Answer

“There are three types of data subsets within a database system. The first one is Data Definition Language or DDL, which allows users to create, alter, or delete objects and perform other various database operations. The second one is Data Manipulation Language or DML, which allows users to query, edit, insert, or delete data. Lastly, Data Control Language or DCL allows administrators to control access to databases.”

Question #6: Describe Both DBMS and RDBMS and How They Differ.

As an SQL developer or database manager, you’re likely familiar with a variety of database management systems, including DBMS and RDBMS. When asked SQL interview questions regarding these two key database management systems, including the following details in your answer:

• A description of both DBMS and RDBMS.
• Similarities between the two database management systems.
• Key differences.

How You Could Answer

“DBMS is short for database management systems. It’s a software system that allows end-users to store, retrieve, access, update, and delete data and run database queries. An RDBMS, also called a relational database management system, is a program that allows users to manage relational databases. While both DBMS and RDBMS are used to manage databases, they both store data differently. For example, DBMS stores data in files, whereas RDBMS stores data in tables and forms.”

Question #7: What Are Tables and Fields in a Database?

When managing databases, you’ll work primarily with tables and fields. Employers will expect you to identify the purpose and functions of tables within a database. Be sure to describe the following when answering SQL interview questions about tables and fields:

• What tables and fields are and how they’re used.
• What type of data typically goes into tables.
• The difference between rows and columns.

How You Could Answer

“Tables and fields are used to store data on specific subjects. Tables logically organize data in rows and columns, much like a spreadsheet. Rows usually contain specific data such as numbers, dates, and dollar amounts, whereas columns contain data categories. Columns also contain field values such as averages and total numbers. Columns represent vertical data. Rows represent horizontal data.”

Question #8: Describe the Difference Between DELETE and TRUNCATE Statements.

DELETE and TRUNCATE are essential SQL commands that are used specifically within tables. While they have some similarities, they are very different. Show employers that you understand the key differences between DELETE and TRUNCATE by including these details in your answer:

• A comparison between the two commands.
• The key functions of each command.
• Which database subset each command belongs to.

How You Could Answer

“Both the DELETE and TRUNCATE commands delete data in tables. However, they serve different purposes. For example, the DELETE command only deletes single rows in a table. The deleted rows can be rolled back. TRUNCATE deletes all rows from a table. But users can’t roll them back once they’re gone. Additionally, DELETE is a DML command and takes more time than TRUNCATE. TRUNCATE is a DDL command and works much quicker than DELETE.”

Question #9: What Is a CASE Statement and Why Is It Used?

CASE statements are a critical part of data analysis and specify field values in tables. A hiring manager may ask you SQL interview questions about how you would use a CASE statement.

Here’s what you should include in your answer:

• Define what a CASE statement is and what it does in a database.
• Discuss the two types of CASE statements and their functions.

How You Could Answer

“A CASE statement is a component of SQL that returns values for specific conditions in database queries that use “Order By” and “Group By” statements. There are two types of CASE statements in SQL. A simple CASE statement uses an expression against multiple values to determine a result. A searched CASE statement, on the other hand, uses a set of Boolean expressions or TRUE and FALSE statements to render a result.”

Question #10: What Are Keys in SQL and How Are They Used?

To be successful in a job where you’ll use SQL, you’ll need an understanding of keys and how to best utilize them in tables. When answering SQL interview questions regarding keys, be sure to discuss the following:

• A definition of SQL keys and their purpose.
• The types of keys used in databases.
• An example of how individual keys work.

How You Could Answer

“SQL keys refer to attributes or sets of attributes that exist in tables. Keys prevent duplicate information from appearing in rows and often link multiple tables within a database. There are generally seven SQL keys: PRIMARY, UNIQUE, CANDIDATE, ALTERNATE, COMPOSITE, SUPER, and FOREIGN. Each of these keys serves a different function. For example, PRIMARY keys and COMPOSITE keys both identify table rows uniquely. However, a PRIMARY key uses only one column, while a COMPOSITE key uses multiple columns.”

Question #11: How Proficient Are You in SQL Server?

Not all SQL interview questions are exclusively technical. Employers will likely ask SQL server interview questions to determine how proficient you are in programs such as Microsoft SQL Server. Be sure to describe these details when answering this question:

• You’re experience with SQL Server.
• Its key functions.
• How you’ve utilized it.

How You Could Answer

“I have about four years of experience using Microsoft SQL Server. I mostly utilized it at my last job. Microsoft SQL Server is one of the best SQL server engines on the market for managing relational database systems. It also provides better data security than any other database management system I’ve used. I’ve used Microsoft SQL Server to process database queries and manage database files, pages, indexes, and tables.”

Question #12: Describe an SQL Query Process.

When answering SQL query interview questions, be sure to include the key steps of running an SQL query and give a brief example. Here’s what you should include in your answer:

• What you need to run an SQL query.
• The type of data you’re looking for.
• How to organize the data in a table.

How You Could Answer

“To run an SQL query, you first need access to a database engine and an SQL client. Once you’re ready to run a query, you need to determine what type of data you’re looking to access. For example, I could use the data to determine the average number of people unemployed in Massachusetts over the last ten years. Then, you’ll need to determine which fields and records you want to display in a table.”

“I would then organize the data in a Group By statement. In the example I’m providing, the columns would represent each county in Massachusetts. The tables would represent the number of people receiving unemployment benefits by year. At the bottom of a column would be a field value calculating the mean unemployment number for each county.”

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