SQL interview questions

 SQL interview questions

SQL Interview Questions

🔰 Basic SQL Interview Questions (For Freshers)

1.    What is SQL?

2.    What is the difference between SQL and MySQL/SQL Server/Oracle?

3.    What are the different types of SQL commands?
(DDL, DML, DCL, TCL, DQL)

4.    What is the difference between DELETE, TRUNCATE, and DROP?

5.    What is a primary key? Can a table have multiple primary keys?

6.    What is a foreign key?

7.    What is the difference between WHERE and HAVING?

8.    What is a join? Name the types of joins.

9.    What is normalization? Explain 1NF, 2NF, 3NF.

10.                       What is a constraint in SQL? Name a few.

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💡 Intermediate SQL Interview Questions

1.    What is the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN?

2.    What is a GROUP BY clause?

3.    What is the use of ORDER BY clause?

4.    What is a subquery? Explain correlated vs non-correlated subqueries.

5.    What are indexes in SQL? How do they improve performance?

6.    What is the difference between UNION and UNION ALL?

7.    What is a view? How is it different from a table?

8.    What is a stored procedure? How is it different from a function?

9.    What is the difference between IS NULL, = NULL, and IS NOT NULL?

10.                       What is a trigger? When would you use one?

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🧠 Advanced SQL Interview Questions

1.    How do you find the second highest salary in a table?

2.    What is a CTE (Common Table Expression)?

3.    How would you optimize a slow-running query?

4.    What is window function in SQL? Explain ROW_NUMBER(), RANK(), DENSE_RANK(), LEAD(), LAG()

5.    What is the difference between clustered and non-clustered index?

6.    How do you handle duplicates in SQL?

7.    What is a transaction? What are ACID properties?

8.    How do you implement pagination in SQL?

9.    How do you perform pivoting and unpivoting in SQL?

10.                       What are temporary tables and table variables?

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🛠️ SQL Query Scenarios

1.    Write a query to fetch duplicate records in a table.

2.    Write a query to get the department with the highest number of employees.

3.    Write a query to find employees who joined in the last 6 months.

4.    Write a query to find the cumulative salary per department.

5.    Write a query to transpose rows into columns.

6.    Write a query to count the number of employees per department having more than 5 employees.

7.    Write a query to get top 3 records per group (e.g., top 3 salaries per department).

8.    Write a query to delete duplicate rows from a table.

9.    Write a query to update a record based on a join.

10.                       Write a query to get all managers who don’t have any subordinates.

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🔐 SQL Security and Admin

1.    What are roles and permissions in SQL Server?

2.    What is SQL injection? How can you prevent it?

3.    What is the difference between GRANT, REVOKE, and DENY?

4.    How do you take a backup and restore a database?

5.    What is the difference between a login and a user in SQL Server?