SQLite Interview Questions and Answers for 5 years experience

1. What is SQLite?

   • Answer: SQLite is a self-contained, serverless, zero-configuration, transactional SQL database engine. It's embedded into applications, meaning it doesn't require a separate server process.

2. What are the advantages of using SQLite?

   • Answer: Advantages include its simplicity, ease of use, lightweight nature, cross-platform compatibility, and the fact it's file-based, requiring no separate server process. This makes it ideal for embedded systems, mobile apps, and applications where a full-blown database server is overkill.

3. What are the disadvantages of using SQLite?

   • Answer: Disadvantages include potential concurrency issues in multi-user environments (though improvements have been made), limited features compared to enterprise-level databases, and potentially slower performance for very large datasets.

4. Explain the concept of a transaction in SQLite.

   • Answer: A transaction is a sequence of one or more SQL statements that are treated as a single logical unit of work. It ensures data integrity; either all statements within a transaction succeed, or none do. SQLite uses ACID properties (Atomicity, Consistency, Isolation, Durability) to guarantee this.

5. How do you begin, commit, and rollback a transaction in SQLite?

   • Answer: You begin a transaction with `BEGIN TRANSACTION`, commit with `COMMIT`, and rollback with `ROLLBACK`.

6. What are indexes in SQLite and why are they important?

   • Answer: Indexes are data structures that improve the speed of data retrieval operations on a database table. They work similarly to an index in a book, allowing for quicker lookups. They are important for improving query performance, especially on large tables.

7. Explain different types of indexes in SQLite.

   • Answer: SQLite supports several index types, including B-tree indexes (the default), unique indexes (ensuring uniqueness of indexed columns), and partial indexes (indexing only specific rows based on a WHERE clause). There are also virtual indexes, which can be used for full-text search.

8. How do you create an index in SQLite?

   • Answer: You use the `CREATE INDEX` statement. For example: `CREATE INDEX idx_name ON mytable (column1, column2);`

9. What is a trigger in SQLite?

   • Answer: A trigger is a procedural code that is automatically executed in response to certain events on a particular table or view, such as INSERT, UPDATE, or DELETE operations.

10. How do you create a trigger in SQLite?

    • Answer: You use the `CREATE TRIGGER` statement. This involves specifying the trigger name, events it responds to, the table it affects, and the SQL code to execute.

11. What are views in SQLite?

    • Answer: A view is a virtual table based on the result-set of an SQL statement. It doesn't store data itself; it provides a customized view of the underlying data.

12. How do you create a view in SQLite?

    • Answer: You use the `CREATE VIEW` statement, specifying the view name and the SQL query that defines it.

13. What is the difference between INTEGER, REAL, and TEXT data types in SQLite?

    • Answer: INTEGER stores integers, REAL stores floating-point numbers, and TEXT stores text strings.

14. What is the `NULL` value in SQLite?

    • Answer: `NULL` represents a missing or unknown value. It's different from an empty string or zero.

15. Explain the concept of constraints in SQLite.

    • Answer: Constraints are rules enforced on data within a table to ensure data integrity. Examples include `NOT NULL`, `UNIQUE`, `PRIMARY KEY`, `FOREIGN KEY`, and `CHECK` constraints.

16. How do you use `JOIN` operations in SQLite?

    • Answer: `JOIN` operations combine rows from two or more tables based on a related column between them. Types include `INNER JOIN`, `LEFT JOIN`, `RIGHT JOIN`, and `FULL OUTER JOIN`.

17. What is a `WHERE` clause in SQLite?

    • Answer: The `WHERE` clause filters the rows returned by a SELECT statement, allowing you to select only rows that meet specific conditions.

18. What is the difference between `GROUP BY` and `ORDER BY` clauses?

    • Answer: `GROUP BY` groups rows with the same values in specified columns into summary rows, like using aggregate functions (SUM, AVG, COUNT). `ORDER BY` sorts the result set based on specified columns.

19. How do you use aggregate functions in SQLite (e.g., SUM, AVG, COUNT)?

    • Answer: Aggregate functions operate on a set of values to compute a single value. They're typically used with `GROUP BY`.

20. What is the purpose of the `LIMIT` clause?

    • Answer: `LIMIT` restricts the number of rows returned by a SELECT statement.

21. How do you handle transactions in a multi-threaded environment using SQLite?

    • Answer: SQLite's file-locking mechanism manages concurrency, but you need careful synchronization within your application code to avoid race conditions and data corruption. Consider using transactions and appropriate locking strategies.

22. Explain the concept of WAL (Write-Ahead Logging) mode in SQLite.

    • Answer: WAL mode improves concurrency by separating the writing of data changes from the updating of the database file itself. This leads to better performance in multi-threaded or multi-process environments.

23. How do you enable WAL mode in SQLite?

    • Answer: You can enable WAL mode using the `PRAGMA journal_mode = WAL;` command.

24. What are some common SQLite error messages you've encountered and how did you resolve them?

    • Answer: [This requires a personalized answer based on your experience. Examples: SQLITE_CONSTRAINT, SQLITE_FULL, SQLITE_BUSY; discuss how you debugged and resolved these in specific situations.]

25. How do you perform data backup and restore in SQLite?

    • Answer: Simple backup involves copying the database file. For more robust backups, consider using `sqlite3` command-line tools or library functions to create a backup copy using `ATTACH` and `DETACH` database functionalities, or utilizing specialized backup utilities.

26. How would you optimize the performance of a slow SQLite query?

    • Answer: Performance optimization involves analyzing the query execution plan, adding indexes, optimizing table structure (normalizing if necessary), using appropriate data types, and ensuring efficient data access patterns.

27. Explain the difference between SQLite and other database systems like MySQL or PostgreSQL.

    • Answer: Key differences include SQLite's serverless architecture, its suitability for embedded systems, its smaller footprint, and its limitations in features and scalability compared to client-server databases like MySQL and PostgreSQL.

28. Describe your experience with using SQLite in a real-world application.

    • Answer: [This needs a personalized answer based on your projects. Detail the application, the role of SQLite, challenges encountered, and solutions implemented.]

29. What are some common security considerations when using SQLite?

    • Answer: Security concerns include protecting the database file from unauthorized access (using appropriate file permissions), sanitizing user inputs to prevent SQL injection vulnerabilities, and considering encryption of the database file itself if sensitive data is involved.

30. How do you handle large datasets in SQLite? What are the limitations?

    • Answer: Handling large datasets involves optimizing queries, using appropriate indexing, and considering database design for efficient querying. Limitations include potential performance bottlenecks, especially without proper optimization and indexing. For extremely large datasets, a more robust database system might be necessary.

31. What are some tools or libraries you've used to work with SQLite?

    • Answer: [List tools like the command-line `sqlite3` utility, database browsers, relevant libraries in various programming languages (Python's `sqlite3`, etc.).]

32. How familiar are you with SQLite's FTS (Full-Text Search) capabilities?

    • Answer: [Describe your knowledge of FTS, its functionalities, and how you've used it (if applicable). Explain the different FTS versions and their features.]

33. Explain your understanding of SQLite's schema.

    • Answer: The SQLite schema defines the structure of the database, including tables, their columns (data types, constraints), indexes, triggers, and views. I understand how to define and manipulate the schema using SQL commands.

34. Describe a time you had to debug a problem related to SQLite. What was the issue, and how did you resolve it?

    • Answer: [Provide a concrete example. Explain the symptoms, your debugging process (using tools, logging, etc.), and the ultimate solution.]

35. How do you ensure data integrity when working with SQLite?

    • Answer: Data integrity is maintained through proper database design (normalization), use of constraints, transactions, and careful error handling in the application code. Regularly backing up the database is also crucial.

36. What are some best practices for using SQLite in a production environment?

    • Answer: Best practices include proper error handling, use of transactions, efficient query design and indexing, regular backups, security considerations (file permissions, input sanitization), and monitoring for performance issues.

37. What is your preferred method for querying data from SQLite and why?

    • Answer: [Explain your preference – command-line, programmatic access (with specific language and library), database browser, etc. – and justify your choice.]

38. Explain how you would approach designing a database schema for a new application using SQLite.

    • Answer: I would start by identifying the entities and their relationships, normalizing the data to reduce redundancy, and choosing appropriate data types for each column. I would then design the tables, including primary and foreign keys, and create indexes for performance optimization.

39. What are some common performance challenges you've encountered while working with SQLite and how did you overcome them?

    • Answer: [Share specific experiences. This could include slow queries due to lack of indexes, poorly designed queries, or large datasets. Discuss the solutions you implemented.]

40. How familiar are you with different SQLite extensions?

    • Answer: [Mention specific extensions you know, such as those for JSON handling, spatial data, or other functionalities. Describe their usage and benefits.]

41. How would you migrate data from another database system to SQLite?

    • Answer: I would use a combination of SQL `EXPORT` or similar functionality from the source database, and SQL `IMPORT` statements in SQLite, potentially involving scripting or ETL tools for complex scenarios and data transformations.

42. How do you handle errors and exceptions when working with SQLite in your chosen programming language?

    • Answer: [Provide a detailed explanation for your chosen language, showing error handling techniques and how to gracefully handle database-related exceptions.]

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