Top 50 SQL Interview Questions to Ask (And Example Answers)
SQL stands for “structured query language.” This is a language used to manage a database. If you work with data, you might need to know how to use SQL queries and how to use them in real life. This article shows you how to answer the top 50 SQL queries interview questions.
Here are some general questions you can use to prepare for your next job interview about SQL queries:
- What do you want to do with SQL queries at this company?
- In three months, what do you think we can do?
- Tell me about how data changes over time.
- Define SQL.
- Why are you quitting your current job?
- Who works with SQL queries and what skills should they have? Why?
- Why should we choose you instead of the other people?
- Have SQL queries helped you get anywhere in your career? Tell me about them, please.
- What salary are you seeking?
- Tell me about a typical day at your dream job.
- Tell me how you explain complicated ideas to a group of people with different levels of knowledge and skills.
- What about you would your last boss say?
- What do you think about working in a place that gives you a lot of freedom?
- How would you tell a team member who made mistakes in a query how to fix them?
Questions about work and history from the past
Interviewers sometimes ask about your background and jobs you’ve had in the past. In an interview, you might be asked these kinds of questions about SQL queries:
- How do you know how to use different kinds of database products?
- When did you first start using SQL?
- Tell me about your past jobs.
- Tell us about the SQL-based projects in your portfolio.
- Have you ever learned about SQL or how to write queries?
- What do you think are the most important ways that SQL queries are used in business?
- Do you know how to write code in any other languages? What are they saying?
- Which part of writing SQL queries do you like the most?
- When did you start working with SQL?
- When you write SQL queries, what do you do well?
- Do you have any weak points in SQL?
- Tell me about a good project you did that used SQL queries.
- What went wrong with a SQL project that didn’t work out?
- Have you ever done anything with DevOps?
- How do you keep track of your SQL projects? What tools do you use?
- How often do you use SQL queries?
In addition to questions about your experience and general questions, you might be asked specific questions that require you to solve SQL problems or answer in multiple steps or actions:
- Prepare sample data from a SQL database using SQL queries.
- Make a query that uses an alias to select mapped data from a table.
- Create a SQL query that sends back a piece of mapped data from the sample table.
- Write a SQL query that only returns unique values from a column of data in a table.
- Make a query to put the first and last names from a sample table into a column called FULL NAME.
- Write a query that will print out the information from a sample table with the first names in ascending order.
- Use a query to find the highest salary for each department in a sample table.
- Print the date right now with a SQL query.
- Using a sample set of data, find all the employee records that have the same first name.
- Return a birth year between 1955 and 1985 for the employee.
- Common SQL queries interview questions and example answers
- Here are common SQL queries interview questions and example answers:
What is a SQL question?
This is the kind of simple question that might come first in a set of SQL interview questions. It asks you to show that you know what a SQL query is and what are its most important parts.
Example: “A query in SQL is a request. It can be a request to get information or to add or change information.”
2. Define subquery
This is a simple question once more. Anyone whose job requires them to work with SQL queries should know how subqueries work. In your answer, give a short, clear definition to show that you understand.
Example: “Subqueries are parts of a query that can be put together. The subquery gives the “inner query,” which is a query that returns part of another query.”
3. Explain how transactions are controlled and what they are.
Transactions are the things that database administrators do every day. Data professionals may need to be able to explain transactions and list important controls.
Example: “Transactions are tasks that happen in a certain order and lead to operations like adding, changing, or deleting records. A transaction has four controls: “commit,” “rollback,” “set traction,” and “savepoint.””
4. Tell me how many comparison operators a subquery can use to compare rows.
People who work with data can use row comparison operators to help them do important tasks for their jobs. Show that you know how to use sequel queries by explaining what row operators are used in a subquery.
“The IN, ANY, and ALL operators can be used to compare rows in subqueries.”
5. Give an example of a stored procedure.
A good way to make a SQL procedure that does more than one thing repeatable is to use a “stored procedure.” Database administrators might have to make these procedural bundles every day, so it’s important that their answer shows they understand.
Example: “A set of SQL statements that can be run when needed, with conditional formatting.”
6. Explain what happens when UNION, MINUS, UNION ALL, and INTERSECT are used.
During a SQL queries interview, you’ll probably have to show that you know how processes work and what they do. To answer this question, explain each one in a few words.
Example: “UNION: Returns any rows that answer the query in more than one way.
MINUS: Returns any rows of data called for by query one, but not by query two.
UNION ALL: This shows all rows that are returned by both queries. The information doesn’t have to be unique, and duplicates are allowed.
INTERSECT: Gives back all rows that are called by both queries and have unique data.”
7. Define index.
Giving a clear explanation of what an index is and how it works with queries. This is a basic question that a data professional should be able to answer.
Example: “An index is a special structure that can be added to a table to speed up queries.”
8. Why is it better to use views in a query?
Using views has many benefits, some of which have to do with queries. Tell me why a data administrator might use views in SQL to manage queries.
“Views can show information from more complicated queries when necessary by using simple data retrieval queries.”
9. Show how to write a query to get information about a worker whose name starts with “M.”
You might have to write practical questions as part of your interview, or you might have to do homework before or after the interview. No matter what, you should review how to write a query so you can answer common SQL queries interview questions.
“SELECT * FROM Student WHERE Employee Name likes ‘M%'” is an example.
10. Look at the differences between nested subqueries and correlated subqueries.
Whenever you are asked to talk about how two things are different, you have the chance to explain two ideas. Take advantage of this by coming up with an answer that shows you know about both.
Example: “A subquery that is nested is one that is inside another subquery. A subquery is said to be correlated if the results of the subquery depend on the values in a query table.”
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