Top 20 SQL Query Interview Questions and Answers in 2024

What is SQL?

SQL full form is a structured Query Language, applied in relational database management systems like MySQL, Sybase, Informix, MS Access, Oracle, and SQL Server.

SQL Interview Questions for Beginners

Q1. What is SQL as a DBMS?

Ans. SQL as a database management system (DBMS) is software managing the creation, usage, and maintenance of databases.

Q2. Can you explain what tables and fields are?

Ans. A table is a data collection with vertical columns and horizontal rows, with specific columns called fields and records.

Q3. What is a join?

Ans. The keyword 'JOINs' is utilized to query data from multiple tables based on their field relationships, emphasizing the significance of keys in JOINs.

Q4. What are the types of SQL Commands?

Ans. SQL commands, including DLC, DDL, DML, and TCL, are essential for database structure generation, manipulation, and management.

Q5. What are aggregate functions in SQL?

Ans. The operations sum, averages, counts, and minimums are crucial for performing calculations on database table groups to extract valuable statistics and metrics.

Q6. What is SQL injection?

Ans. SQL Injection is a malicious way by which an attacker injects SQL queries for unauthorized access to a database or data manipulation.

Q7. What is denormalization?

Ans. Denormalization in SQL consolidates data from related tables, improving query performance and speed. It's useful for data retrieval, reporting, and real-time consistency, but should be cautiously used.

Q8. What is Data mining?

Ans. Utilizing SQL queries to analyze big data sets helps organizations identify trends and patterns, and relationships, thereby aiding in informed decision-making.

Q9. Explain a data warehouse?

Ans. A centralized system that manages and retrieves volumes of data from multiple sources, integrating databases and applications for analytical reporting and decision-making.

Q10. Explain the ACID properties in a database?

Ans. ACID properties ensure data reliability and consistency in SQL systems, preventing concurrent transactions and ensuring data integrity.

SQL Interview Questions for experienced

Q11. Differentiate between the INNER JOIN and LEFT JOIN?

Ans. INNER JOIN returns rows where a match exists in both tables. Whereas, the LEFT JOIN returns all rows from the left table and matching rows from the right table, if no match exists.

Q12. How to identify duplicate records in a table?

Ans. Use a GROUP BY clause and the COUNT() method to get records whose counts are more than one, or a self-join to compare comparable values.

Q13. How do functions and a stored procedure differ?

Ans. A function is a set of SQL statements that performs a specific operation. Whereas, the pre-compiled set of SQL statements is the stored procedure.

Q14. How do you improve a slow SQL query?

Ans. Create column indexes, optimize queries with efficient joins, identify bottlenecks using EXPLAIN, denormalize data for enhanced efficiency, and adjust database server parameters.

Q15. Explain common table expression (CTE)?

Ans. A CTE is a temporary named result set used in SELECT, INSERT, UPDATE, or DELETE statements to simplify complex queries and improve readability.

Q16. Why is the HAVING clause used?

Ans. The HAVING clause filters groups based on specific criteria, working with aggregated data like the WHERE clause, but only after grouping the data.

Q17. How does a stored procedure and a function in SQL differ?

Ans. A pre-compiled set of SQL statements is capable of performing complex tasks like DML and DDL, while a function is a named block that returns a single value.

Q18. Why is the GROUP BY clause used?

Ans. It is utilized to group rows with identical values into summary rows, which are then aggregated using functions like COUNT, SUM, and AVG.

Q19. Explain the full-text searching in SQL databases?

Ans. The natural language query efficiently searches large text fields, enabling specific word or phrase searches, proximity searches, and fuzzy matching, with improved search performance through indexes.

Q20. Define MERGE statement?

Ans. It is a tool that performs multiple DML operations (INSERT, UPDATE, DELETE) in a single statement based on a specified condition.

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Conclusion

There are more than 50 SQL questions available across multiple platforms. However, the most crucial interview questions and answers are listed above. The benefits of SQL course may be utilized in a variety of industries, including technology, banking, and retail. The SQL course provides a fulfilling job.

FAQS

Q1: Is it worth taking an online SQL course?

A1. Online SQL courses are an effective approach to enhance or learn new SQL abilities.

Q2. Are beginner SQL developer courses useful?

A2. Beginner SQL developer courses are useful for employee training and skill enhancement.

Q3. Is the SQL course easy?

A3. The training is simple to understand, with industry professionals aimed at each student's needs.

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A4. SQL knowledge is valuable in various sectors like finance, marketing, healthcare, and more.

Q5. What are the career paths after an SQL course?

A5. SQL Developer and data analyst are some of the career paths.

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