SQLite Interview Questions and Answers for 7 years experience

1. What is SQLite and why is it different from other database systems?

   • Answer: SQLite is a serverless, embedded, relational database management system. Unlike other database systems like MySQL or PostgreSQL that run as separate server processes, SQLite is integrated directly into the application. This means it doesn't require a separate server to manage the database, making it lightweight and easy to deploy. Its file-based nature simplifies deployment and management, but also limits scalability compared to client-server databases.

2. Explain the advantages and disadvantages of using SQLite.

   • Answer: Advantages: Lightweight, easy to embed in applications, no server configuration required, cross-platform compatibility, simple to use, ACID compliant (atomicity, consistency, isolation, durability). Disadvantages: Limited scalability, potential for data corruption if not handled carefully, no built-in replication or clustering features, less robust security compared to server-based databases.

3. Describe the different data types supported by SQLite.

   • Answer: SQLite has a relatively simple type system. It has INTEGER, REAL, TEXT, BLOB, and NULL. While it supports type affinity, it's dynamically typed at runtime. This means you can store different types of data in a column designed for one specific type, though this might impact performance and data integrity if not managed properly.

4. How do you create a table in SQLite? Provide an example.

   • Answer: You use the `CREATE TABLE` statement. For example: `CREATE TABLE users (id INTEGER PRIMARY KEY, username TEXT UNIQUE, email TEXT, password TEXT);` This creates a table named `users` with columns for ID (primary key), username (unique), email, and password.

5. Explain the concept of primary keys and foreign keys in SQLite.

   • Answer: A primary key uniquely identifies each row in a table. It cannot contain NULL values. A foreign key establishes a link between two tables. It references the primary key of another table, ensuring referential integrity. This prevents orphaned records and maintains data consistency.

6. How do you insert data into an SQLite table? Provide an example.

   • Answer: Use the `INSERT INTO` statement. For example: `INSERT INTO users (username, email, password) VALUES ('johnDoe', 'john.doe@example.com', 'password123');` This inserts a new row into the `users` table.

7. How do you update data in an SQLite table? Provide an example.

   • Answer: Use the `UPDATE` statement. For example: `UPDATE users SET email = 'john.updated@example.com' WHERE username = 'johnDoe';` This updates the email address for the user 'johnDoe'.

8. How do you delete data from an SQLite table? Provide an example.

   • Answer: Use the `DELETE FROM` statement. For example: `DELETE FROM users WHERE id = 1;` This deletes the row with ID 1 from the `users` table.

9. Explain the different types of JOINs in SQL and provide examples using SQLite.

   • Answer: INNER JOIN (returns rows only when there is a match in both tables), LEFT JOIN (returns all rows from the left table and matching rows from the right table), RIGHT JOIN (returns all rows from the right table and matching rows from the left table), FULL OUTER JOIN (returns all rows from both tables, matching where possible – not directly supported in SQLite but can be simulated using UNION). Examples would involve joining two tables based on a common column using the appropriate `JOIN` keyword and `ON` clause specifying the join condition.

10. How would you handle transactions in SQLite?

    • Answer: SQLite supports transactions using `BEGIN TRANSACTION`, `COMMIT`, and `ROLLBACK`. `BEGIN TRANSACTION` starts a transaction, `COMMIT` saves all changes made within the transaction, and `ROLLBACK` undoes all changes. Transactions ensure data consistency.

11. What are indexes in SQLite and how do they improve query performance?

    • Answer: Indexes are data structures that improve the speed of data retrieval. They work by creating a sorted lookup table for a specific column (or set of columns). This allows SQLite to quickly locate rows that match a given search criterion, avoiding a full table scan.

12. Explain the difference between `LIKE` and `GLOB` operators in SQLite.

    • Answer: Both are used for pattern matching. `LIKE` uses SQL standard wildcard characters (`%` and `_`), while `GLOB` uses shell-style wildcards (`*` and `?`). `GLOB` is generally faster for simple patterns.

13. How do you handle NULL values in SQLite?

    • Answer: Use `IS NULL` or `IS NOT NULL` in your `WHERE` clauses to test for NULL values. Avoid using `=` or `!=` with NULL values as they will always return false.

14. How can you enforce data integrity in SQLite databases?

    • Answer: Use constraints like `NOT NULL`, `UNIQUE`, `PRIMARY KEY`, `FOREIGN KEY`, `CHECK`, and `DEFAULT` to ensure data validity and consistency. Properly designed database schema and well-defined transactions also contribute to data integrity.

15. Describe your experience with SQLite's built-in functions.

    • Answer: (This requires a personalized response based on your actual experience with specific SQLite functions like `SUM`, `AVG`, `COUNT`, `MAX`, `MIN`, `DATE`, `STRFTIME`, etc.)

16. How do you optimize SQLite queries for performance?

    • Answer: Use appropriate indexes, avoid `SELECT *`, use `EXPLAIN QUERY PLAN` to analyze query execution, optimize table design, ensure data types are appropriate, and consider using appropriate aggregate functions.

17. How would you handle large datasets in SQLite?

    • Answer: For very large datasets, SQLite might not be the optimal choice. Consider alternatives like client-server databases. However, optimization techniques such as proper indexing, efficient queries, and using `VACUUM` to reduce database size can help improve performance with larger datasets, but there are inherent limitations.

18. What are some common issues you've encountered when working with SQLite and how did you resolve them?

    • Answer: (This requires a personalized response detailing specific problems, such as database locking issues, performance bottlenecks, or data corruption, and the solutions implemented).

19. Explain your experience with using SQLite in different programming languages (e.g., Python, Java, C++).

    • Answer: (This requires a personalized response detailing the specific languages and libraries used, along with examples of how SQLite was integrated into applications).

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