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50+ SQL Interview Questions and Tips on How to Crack Them

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50+ SQL Interview Questions and Tips on How to Crack Them
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SQL interview questions are a critical piece of technical interviews and coding interviews. Most engineering roles, such as software engineer, data scientist, and data engineer, require SQL as a secondary skill. So, when you’re preparing for technical interviews, it is a good practice to prepare basic SQL questions. Some companies conduct separate SQL interview rounds for roles like data engineer and data scientist.

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To help you with your SQL interview preparation, we’ve gathered some frequently asked SQL interview questions. Here’s what we’ll discuss in this article:

  • Why Is SQL So Popular?
  • Types of SQL Commands
  • Types of Questions Asked in SQL Interviews
  • PL/SQL Interview Questions
  • Advanced SQL Interview Questions
  • SQL Interview Questions Asked by FAANG Companies
  • How to Prepare for SQL Interviews
  • SQL Interview FAQs

Why Is SQL So Popular?

SQL stands for Structured Query Language, a domain-specific language for managing data in the Database Management System (DBMS). Database Management System is a software that handles the creation, updation, and management of data. 

SQL is one of the most desired skills in the market, as there is a massive usage of DBMS in every software. Every application or software you develop has some data associated with it and needs the DBMS principles to manage it.

Types of SQL Commands

There are basically five different types of commands in SQL:

  1. Data Definition Language (DDL) Commands: We use DDL Commands to define the database schema, change the structure of the table by creating, modifying, or deleting the columns. Commands like CREATE, DROP, ALTER, and TRUNCATE are some of the DDL commands.
  2. Data Manipulation Language (DML) Commands: We use DML commands to manipulate the data present in the database. Commands like INSERT, UPDATE, and DELETE are some of the DML commands.
  3. Data Control Language (DCL) Commands: We use DCL commands to grant and revoke access to database users. Commands like GRANT and REVOKE are some DCL commands. 
  4. Transaction Control Language (TCL) Commands: We use TCL Commands alongside DML commands to save, undo, or rollback to a given save point. Commands like COMMIT, ROLLBACK, and SAVEPOINT are some of the TCL Commands. 
  5. Data Query Language (DQL) Commands: We use DQL Command to fetch the data from the database. For now, there is only one DQL Command that is the SELECT statement.

Types of Questions Asked in SQL Interviews

In SQL Interviews, you can expect various questions to define terms, describe, or form a query. Here are some examples:

1. Define a Term

Some basic SQL interview questions are about defining a term in SQL. The interviewer may ask you to explain some technical concepts, explain the differences between two concepts, or explain how a concept works. 

Following are some of the terms you should be familiar with to answer these SQL interview questions successfully:

  • Primary Key, Foreign Key, and Unique Key
  • RDBMS vs. DBMS
  • Constraints
  • Cursors
  • Normalization vs. Denormalization
  • Index
  • Triggers
  • Clustered vs. Non-Clustered Index

Sample SQL Interview Questions on Defining Terms

  1. Explain the types of Joins in SQL.
  2. What are the DDL Statements in SQL?
  3. Explain the differences between DROP, TRUNCATE, and DELETE Statements.
  4. What is the difference between WHERE clause and HAVING clause?
  5. What is an Index? Explain the different types of Index.
  6. What is the difference between RANK() and DENSE_RANK() functions in SQL?
  7. What are Entities and Relationships?
  8. What are the different types of Normalization?
  9. What are UNION, MINUS, and INTERSECT commands?
  10. How do you use a Cursor?

2. Questions About a Query

In this type of SQL interview question, the interviewer will give a SQL query and ask some questions about it. Your answers to such questions convey your ability to read and interpret queries written by others.

Sample SQL Interview Questions About Queries

  1. Find the error in the query.
  2. Explain what the query is written for.
  3. Does the query return an output?
  4. Rectify the error in the query.
  5. Find if there is any other way to perform the same functionality the query is currently performing.
  6. Change the ORDER BY Clause and predict the outcome.

3. Write a Query

These are the most common questions asked in SQL Interviews. Here, the interviewer will give the details of some tables and ask you to retrieve, update, or remove the data from those tables. The difficulty of these questions might vary based on the role you’re applying for. But, you can expect to get some questions on the following topics, statements, and clauses:

  • Modifying a Database (Using INSERT, UPDATE, DELETE)
  • SubQueries
  • Joining Tables (Using Inner, Left, Right Joins)
  • Organizing Data (ORDER BY, GROUP BY, HAVING Clauses)
  • Categorization and Aggregation (CASE, COUNT, SUM)

Sample SQL Interview Questions on Writing a Query 

  1. Write a query to remove duplicates in a table without creating another table.
  2. Write a query to get the third-highest salary of an employee without using TOP or LIMIT keywords.
  3. List all the ways to get the count of records in a table.
  4. Write a SQL Query to fetch only the odd rows from a table.
  5. Write a query to fetch records present in one table but not in another table.
  6. Write a query to fetch the position of a given character in a field.
  7. Write a query to join two tables having duplicate values.
  8. Write a query to join two tables containing multiple NULL values.
  9. Write a query using UNION ALL that uses a WHERE clause to eliminate duplicates.
  10. Write a query to explain the usage of NVL and NVL2 functions.

PL/SQL Interview Questions

PL/SQL is an extension of SQL used in Oracle’s relational database. With PL/SQL, you can create powerful queries by combining the manipulation power of SQL and the processing power of procedural language.

Here are some popular interview questions on PL?SQL:

  1. What are the features of PL/SQL?
  2. Explain the basic structure followed in PL/SQL.
  3. What is a Trigger? Explain with some examples where Trigger can be used.
  4. Explain PL/SQL execution architecture.
  5. How do you debug your PL/SQL code?
  6. Write a PL/SQL program to calculate the sum of the digits of a number.
  7. Write a PL/SQL program to convert each digit of a given number to its corresponding word format.
  8. Write a PL/SQL program to calculate the average of the numbers entered by the user. Stop the entry of numbers when the user enters 0.
  9. Write a PL/SQL program to count the number of Sundays between two given dates.
  10. Write a PL/SQL program to find whether a given string is a palindrome or not.

Advanced SQL Interview Questions

  1. Mention some advantages and disadvantages of using Synonyms.
  2. Explain scalar subqueries and correlated subqueries.
  3. What are Common Table Expressions (CTE)?
  4. What do you do when you forget your root password?
  5. Explain Denormalization.
  6. What are magic tables? How are they useful in Triggers?
  7. Write a query to split a string into multiple columns.
  8. How to display the following output using a query?
    *
    **
    ***
  9. Write a query to add email validation in a single query.
  10. Write a query to display a date column in YYYY-DAY-DATE format.

Read Facebook SQL Interview Questions to understand what kind of SQL interview questions you can expect at Facebook tech interviews. 

SQL Interview Questions Asked by FAANG Companies

  1. Write a query to find the number of customers who placed an order and the average order amount.
  2. Write a query to display cities with higher than average home prices when compared to the national average. 
  3. Write a query to display the users and distance traveled of the top 10 users who have traveled the greatest distance.
  4. What is the difference between DELETE and TRUNCATE?
  5. Explain how you would build a recommendation system.
  6. Consider two tables:
    1) Product Table: Id, Product_name, Manufacturer_id
    2) Manufacturer Table: Id, Manufacturer
    There are 8 records in the first table and 4 records in the second table. How many rows will the given query return?
  7. Write a query to find the nominee who has won the most Oscars. Display the nominee’s name with the number of Oscars. Order the result based on the number of wins in descending order.

You can also head over to Amazon SQL Interview Questions for some SQL questions asked in Amazon Interviews. 

7 Tips to Crack SQL Interview Questions

Follow these proven tips to answer and nail SQL interview questions:

1. Ask Questions

When the interviewer asks a question, take some time to understand the questions completely and ask clarifying questions if necessary. Know the datatypes of the columns present, if there are any primary keys etc.

2. Identify the Relevant Columns 

You don’t require all the columns present in the table for your output. Identify the columns you need to work on, so you can concentrate on those.

3. Think About What Your Final Answer Should Look Like

While trying to solve the problem, keep the answer in your mind. Imagine what your final output should look like. This helps you to clear your mind and think about the logical ways to solve the problem. 

4. Solve the Query One Step at a Time

Break down the problem into subparts and solve them one step at a time. If you have subqueries, start by solving the subquery first and then think about the main query. It helps you to concentrate on bits of the problem rather than the problem as a whole.

5. Include Comments

Include comments to explain what each step of your query performs. It helps you and the interviewer to understand the code and enables you to keep track of where you are.

6. Use Formatting

While you’re writing queries on a notebook, whiteboard, or sharing your screen, it’s essential to make the interviewer understand the query. Formatting the query helps the code look neat and concise and allows the interviewer to understand the code even before explaining it.

7. Talk Through the Process

It’s important to explain to the interviewer what you’re doing. It helps them understand how you approach a problem and give some tips if you’re stuck anywhere. So, make sure to explain what, why, and how of each step.

SQL Interview FAQs

1. Is SQL hard to learn?

SQL is considered to be one of the easiest languages to learn. The syntax is similar to plain English, which makes it easy to read and understand. 

2. Why do you use SQL?

SQL is used to communicate with Databases. It is used to access, read, update, and delete data from the Database. 

3. Is SQL important for Interviews?

SQL skills are highly desirable in the market due to the massive use of DBMS in almost all the software being developed. 

4. What are the basic SQL Commands?

SQL Commands are broadly classified into five categories. They are Data Definition Language, Data Manipulation Language, Data Query Language, Data Control Language, and Transaction Control Language, each having a separate functionality. 

5. How do I prepare for an SQL interview?

To prepare for SQL interviews, you must first understand the types of questions asked during the interview. These include questions related to defining a term, questions about a given query, and questions that will require you to write a query. Practice questions from each category, and while practicing, be sure to follow the tips given in this article to structure your answers.

Are You Ready to Nail Your Next Tech Interview?

Since its inception in 2014, Interview Kickstart has helped thousands of experienced engineers realize their true calling. We aim to help engineers get better acquainted with the intricacies of their chosen field and provide them with all the guidance they need to clear interviews with tech giants. 

Knowing very well that clearing an interview requires much more than sound technical knowledge, we train you in a manner that helps you develop a winner's stride. IK is your golden ticket to land the job you deserve.

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