Here are the interview questions and answers for SQL Developer Jobs in the USA;

1. What is SQL?

• SQL stands for Structured Query Language. It is a domain-specific language used for managing and manipulating relational databases.

2. What are the different types of SQL statements?

• SQL statements include SELECT (retrieve data), INSERT (add records), UPDATE (modify records), DELETE (remove records), and others.

3. Explain the difference between INNER JOIN and LEFT JOIN.

• INNER JOIN returns only the matching rows in both tables, while LEFT JOIN returns all rows from the left table and the matching rows from the right table.

4. What is normalization?

• Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity.

5. What is denormalization?

• Denormalization involves combining tables or reintroducing redundancy to improve query performance.

6. Explain the primary key.

• A primary key is a unique identifier for a record in a table. It ensures that each record is uniquely identified within the table.

7. What is a foreign key?

• A foreign key is a field that links to the primary key in another table, establishing a relationship between the two tables.

8. What is an index?

• An index is a data structure that improves the speed of data retrieval operations on a database table.

9. Differentiate between clustered and non-clustered indexes.

• A clustered index determines the physical order of data in a table, while a non-clustered index does not alter the physical order of the table.

10. Explain ACID properties in the context of databases.

• ACID stands for Atomicity, Consistency, Isolation, and Durability. It ensures the reliability of database transactions.

11. How is the DISTINCT keyword used in SQL?

• The DISTINCT keyword is used to retrieve unique values from a specified column in a table.

12. What is the difference between CHAR and VARCHAR data types?

• CHAR is a fixed-length character data type, while VARCHAR is a variable-length character data type.

13. Explain the GROUP BY clause.

• The GROUP BY clause is used to group rows that have the same values in specified columns into summary rows.

14. How can you prevent SQL injection?

• Use parameterized queries or prepared statements to prevent SQL injection by avoiding direct insertion of user input into SQL statements.

15. What is a stored procedure?

• A stored procedure is a set of SQL statements with a name that is stored in the database and can be called by other programs.

16. What is the difference between a view and a table?

• A table is a storage structure, while a view is a virtual table based on the result of a SELECT query.

17. Explain the HAVING clause.

• The HAVING clause is used in combination with the GROUP BY clause to filter the results of aggregate functions.

18. What is the purpose of the SQL ORDER BY clause?

• The ORDER BY clause is used to sort the result set of a query in ascending or descending order.

19. What is a trigger?

• A trigger is a set of instructions that are automatically executed or fired in response to certain events on a particular table or view.

20. How do you perform a backup and restore in SQL Server?

• Use the BACKUP DATABASE and RESTORE DATABASE commands to perform backup and restore operations in SQL Server.

21. Explain the difference between UNION and UNION ALL.

• UNION combines the result sets of two SELECT statements and removes duplicates, while UNION ALL includes all rows, including duplicates.

22. What is the purpose of the SQL CASE statement?

• The CASE statement is used to perform conditional logic within a SQL query.

23. How can you retrieve the top N records from a table?

• Use the TOP or LIMIT clause to retrieve the top N records from a table.

24. What is a self-join?

• A self-join is a regular join, but the table is joined with itself.

25. How do you optimize a SQL query?

• Optimize a query by using indexes, avoiding SELECT * in queries, and optimizing the WHERE clause conditions. Additionally, consider denormalization for performance improvement.