SQLite Interview Questions and Answers for internship

1. What is SQLite?

   • Answer: SQLite is a self-contained, serverless, zero-configuration, transactional SQL database engine. It's embedded into applications and 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 that it doesn't require a separate server process, making it ideal for embedded systems and applications where resource constraints are a factor.

3. What are the disadvantages of using SQLite?

   • Answer: Disadvantages include potential performance limitations for very large databases, lack of advanced features found in client-server databases, and concurrency issues if not handled carefully.

4. Explain the concept of ACID properties in SQLite.

   • Answer: ACID stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure that database transactions are processed reliably. Atomicity means a transaction is treated as a single unit; either all changes are committed, or none are. Consistency ensures that transactions maintain data integrity. Isolation guarantees that concurrent transactions appear to execute serially. Durability means that once a transaction is committed, the changes are permanent even in case of a system failure.

5. How does SQLite handle transactions?

   • Answer: SQLite uses `BEGIN TRANSACTION`, `COMMIT`, and `ROLLBACK` statements to manage transactions. `BEGIN TRANSACTION` starts a transaction, `COMMIT` saves changes, and `ROLLBACK` undoes changes.

6. What is a database schema?

   • Answer: A database schema is a formal description of the structure of a database. It defines the tables, columns, data types, constraints, and relationships between different parts of the database.

7. Explain different data types supported by SQLite.

   • Answer: SQLite supports several data types including INTEGER, REAL, TEXT, BLOB, and NULL. While it's dynamically typed, these types offer hints for storage and efficiency.

8. 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 at the cost of additional writes and storage space to maintain the index data structure. They are crucial for optimizing query performance, especially on large tables.

9. How do you create an index in SQLite?

   • Answer: You create an index using the `CREATE INDEX` statement. For example: `CREATE INDEX idx_name ON mytable (column1, column2);` creates an index named `idx_name` on columns `column1` and `column2` of table `mytable`.

10. Explain the difference between `WHERE` and `HAVING` clauses.

    • Answer: `WHERE` filters rows *before* grouping, while `HAVING` filters rows *after* grouping (using aggregate functions like `SUM`, `AVG`, `COUNT`, etc.).

11. What are JOINs in SQL and what are the different types?

    • Answer: JOINs combine rows from two or more tables based on a related column between them. Common types include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN (though FULL OUTER JOIN isn't directly supported in SQLite, it can be simulated).

12. How do you use subqueries in SQLite?

    • Answer: Subqueries are queries nested within another query. They can be used in the `SELECT`, `FROM`, `WHERE`, and `HAVING` clauses to retrieve data based on the results of the inner query.

13. Explain the use of aggregate functions in SQLite.

    • Answer: Aggregate functions perform calculations on a set of values and return a single value. Examples include `COUNT`, `SUM`, `AVG`, `MAX`, `MIN`.

14. How do you handle NULL values in SQLite?

    • Answer: NULL represents the absence of a value. Use `IS NULL` and `IS NOT NULL` in `WHERE` clauses to check for NULL values. Aggregate functions often ignore NULLs.

15. What are constraints in SQLite? Give examples.

    • Answer: Constraints enforce data integrity. Examples include `NOT NULL`, `UNIQUE`, `PRIMARY KEY`, `FOREIGN KEY`, `CHECK`.

16. How do you create a table in SQLite?

    • Answer: Use the `CREATE TABLE` statement, specifying column names, data types, and constraints. Example: `CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT, email TEXT UNIQUE);`

17. How do you insert data into a SQLite table?

    • Answer: Use the `INSERT INTO` statement. Example: `INSERT INTO users (name, email) VALUES ('John Doe', 'john.doe@example.com');`

18. How do you update data in a SQLite table?

    • Answer: Use the `UPDATE` statement. Example: `UPDATE users SET email = 'john.updated@example.com' WHERE id = 1;`

19. How do you delete data from a SQLite table?

    • Answer: Use the `DELETE FROM` statement. Example: `DELETE FROM users WHERE id = 1;`

20. What is a transaction in the context of databases?

    • Answer: A transaction is a sequence of database operations performed as a single logical unit of work. Either all operations succeed, or none do, maintaining data integrity.

21. Explain the different levels of transaction isolation.

    • Answer: Different isolation levels control how transactions interact with each other. Read Uncommitted, Read Committed, Repeatable Read, and Serializable are common levels, each offering varying degrees of protection against concurrency issues.

22. How do you manage concurrency in SQLite?

    • Answer: SQLite uses file-level locking to manage concurrency. Transactions and proper isolation levels are key to preventing data corruption in multi-user environments.

23. What are the different ways to connect to a SQLite database from a programming language?

    • Answer: Many languages have libraries for connecting to SQLite, such as the `sqlite3` module in Python, or the appropriate JDBC driver in Java.

24. How would you optimize a slow SQLite query?

    • Answer: Techniques include adding indexes, optimizing the `WHERE` clause, using `EXPLAIN QUERY PLAN` to analyze the query execution plan, and ensuring efficient data types are used.

25. What is the role of the `PRAGMA` command in SQLite?

    • Answer: The `PRAGMA` command is used to configure various aspects of the database, such as setting the cache size, enabling or disabling features, and retrieving database information.

26. Explain the concept of a database trigger in SQLite.

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

27. What are views in SQLite? How are they useful?

    • Answer: Views are virtual tables based on the result-set of an SQL statement. They provide a simplified or customized view of the underlying data, enhancing data security and simplifying queries.

28. How can you backup and restore a SQLite database?

    • Answer: A simple way is to copy the database file. For more advanced backups, consider using tools that support creating backups with transaction logs for point-in-time recovery.

29. What is a foreign key constraint and how is it used?

    • Answer: A foreign key establishes a link between two tables, enforcing referential integrity. It ensures that values in a foreign key column in one table match values in the primary key column of another table.

30. How do you handle errors in SQLite operations?

    • Answer: Error handling depends on the programming language and its SQLite library. Generally, exceptions or return codes indicate errors; appropriate handling mechanisms must be used.

31. What is the difference between `AUTOINCREMENT` and `rowid` in SQLite?

    • Answer: `rowid` is a unique 64-bit integer automatically assigned to each row by SQLite. `AUTOINCREMENT` provides a similar but more controlled mechanism for generating unique sequential integer values for a column.

32. Explain the concept of a full-text search in SQLite.

    • Answer: SQLite's full-text search capabilities enable efficient searching within text data, using features like MATCH, rank, and various options for matching and scoring.

33. How can you improve the performance of SQLite on mobile devices?

    • Answer: Techniques include proper indexing, using appropriate data types, optimizing queries, and managing the database cache effectively.

34. Describe your experience working with SQL databases (if any).

    • Answer: [Candidate should provide a detailed answer based on their personal experience. If they lack experience, they should mention relevant coursework or projects.]

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

    • Answer: Security concerns include controlling access to the database file, validating user inputs to prevent SQL injection, and ensuring the application's security practices (e.g., proper authentication and authorization) are robust.

36. How would you troubleshoot a corrupted SQLite database?

    • Answer: Steps include trying to open the database and checking error messages, using SQLite's built-in tools for database repair (if applicable), and potentially restoring from a backup.

37. What is the purpose of the `LIMIT` clause in SQL?

    • Answer: `LIMIT` restricts the number of rows returned by a query, useful for pagination or retrieving a subset of results.

38. What is the `OFFSET` clause and how does it work with `LIMIT`?

    • Answer: `OFFSET` specifies the starting row for `LIMIT`. `LIMIT n OFFSET m` returns n rows starting from row m+1.

39. Explain the use of the `ORDER BY` clause.

    • Answer: `ORDER BY` sorts the result set of a query based on one or more columns in either ascending or descending order.

40. What is the difference between `COUNT(*)` and `COUNT(column_name)`?

    • Answer: `COUNT(*)` counts all rows, including those with NULL values. `COUNT(column_name)` counts only rows where the specified column is NOT NULL.

41. How do you use `LIKE` operator for pattern matching in SQLite?

    • Answer: The `LIKE` operator matches text patterns using wildcards `%` (any sequence of characters) and `_` (any single character).

42. What are the different ways to perform string concatenation in SQLite?

    • Answer: The `||` operator concatenates strings. The `CONCAT` function can also be used.

43. How do you use date and time functions in SQLite?

    • Answer: SQLite provides various functions for working with dates and times, such as `DATE`, `TIME`, `DATETIME`, `STRFTIME`, etc. The specific functions and their formats need to be consulted in the documentation.

44. Explain the concept of a database vacuum in SQLite.

    • Answer: A database vacuum reclaims disk space by removing unused pages from the database file, improving performance and reducing file size.

45. What are some common performance bottlenecks in SQLite?

    • Answer: Potential bottlenecks include lack of indexing, inefficient queries, excessive data volume, inappropriate data types, and I/O limitations.

46. How do you handle large datasets in SQLite?

    • Answer: Strategies include proper indexing, query optimization, using appropriate data types, potentially partitioning data into multiple tables, and considering alternative database solutions if performance remains inadequate.

47. What is your preferred method for debugging SQLite queries?

    • Answer: [Candidate should describe their preferred debugging methods, which might include using `EXPLAIN QUERY PLAN`, print statements, logging, debuggers, or other tools.]

48. Are you familiar with any SQLite extensions or add-ons?

    • Answer: [Candidate should mention any extensions they are familiar with, such as extensions that provide full-text search functionality beyond the built-in features, or other specialized extensions.]

49. What are your strengths and weaknesses related to database management?

    • Answer: [Candidate should provide a self-assessment of their skills, highlighting both strengths and areas for improvement in database management.]

50. Why are you interested in this SQLite internship?

    • Answer: [Candidate should articulate their reasons, demonstrating their interest in the specific technologies and the opportunity to learn and contribute.]

51. What are your salary expectations?

    • Answer: [Candidate should answer this question honestly and realistically based on their research and experience level.]

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