Top SQL Interview Questions and Answers for Beginners & Intermediate Practitioners

In today’s tech-driven job market, SQL (Structured Query Language) skills are in high demand, especially for roles in data analysis, database administration, and software development. Whether you’re a seasoned professional or just starting your career journey, preparing for SQL interview questions is crucial. To help you ace your next interview, let’s delve into some common SQL interview questions and strategies to tackle them effectively.

1. What is SQL, and what are its primary functions?

SQL, or Structured Query Language, is a standard programming language used for managing and manipulating relational databases. Its primary functions include data retrieval, insertion, updating, and deletion. SQL enables users to interact with databases to perform various operations such as querying, modifying, and managing data.

2. Differentiate between SQL and MySQL.

SQL is a standard language used for managing relational databases, while MySQL is an open-source relational database management system (RDBMS) that uses SQL as its primary language. MySQL is one of many database management systems that support SQL.

3. Explain the difference between DELETE and TRUNCATE commands.

DELETE command is used to remove rows from a table based on specified criteria, whereas TRUNCATE command is used to remove all rows from a table, effectively resetting the table to its original state. DELETE command can be rolled back using a transaction, while TRUNCATE is not transactional and cannot be rolled back.

4. What is a primary key, and why is it important?

A primary key is a column or a set of columns that uniquely identifies each row in a table. It ensures data integrity and helps enforce entity integrity by preventing duplicate or null values in the primary key column(s). Primary keys are essential for maintaining data consistency and establishing relationships between tables in a relational database.

5. What is a foreign key, and how is it different from a primary key?

A foreign key is a column or a set of columns in a table that establishes a relationship with the primary key of another table. It ensures referential integrity by enforcing a link between the two tables. Unlike a primary key, a foreign key can contain duplicate values and null values, and it does not have to be unique within the table.

6. Describe the difference between INNER JOIN and LEFT JOIN.

INNER JOIN returns only the rows that have matching values in both tables based on the specified join condition. It excludes unmatched rows from both tables. LEFT JOIN returns all the rows from the left table and the matched rows from the right table. If there are no matching rows in the right table, NULL values are returned for the columns of the right table.

7. Explain the ACID properties in the context of database transactions.

ACID stands for Atomicity, Consistency, Isolation, and Durability, which are the four key properties that ensure reliability and integrity of database transactions.

• Atomicity ensures that a transaction is treated as a single unit of work, either all of its operations are completed successfully, or none of them are.
• Consistency ensures that the database remains in a consistent state before and after the transaction, maintaining integrity constraints and rules.
• Isolation ensures that the concurrent execution of transactions does not interfere with each other, preventing data corruption and ensuring transaction integrity.
• Durability ensures that once a transaction is committed, its changes are permanent and persistent, even in the event of system failures or crashes.

Conclusion:

Preparing for SQL interview questions requires a solid understanding of database concepts, SQL syntax, and query optimization techniques. By familiarizing yourself with common SQL interview questions and practicing your skills, you can confidently demonstrate your expertise and land your dream job in the competitive tech industry.

For more SQL interview practice, check out CourseAI for interactive quizzes and exercises.