Top25 Interview Questions and Answers for IBM DB2 Developer

IBM DB2 is one of the most powerful and widely used relational database management systems, especially in enterprise environments such as banking, insurance, retail, and telecom. Whether you are a fresher preparing for your first DB2 interview or an experienced professional looking to refresh your knowledge, this blog covers the top 25 IBM DB2 developer interview questions with detailed answers.

1. What is IBM DB2?

IBM DB2 is a relational database management system (RDBMS) developed by IBM. It supports SQL standards and is designed for high availability, scalability, and performance. DB2 runs on multiple platforms including Linux, UNIX, Windows, and mainframes (z/OS).

Key features include:

• High-speed data processing
• Advanced security
• Support for OLTP and OLAP workloads
• Integration with IBM tools and cloud platforms

2. What are the different editions of DB2?

IBM DB2 is available in multiple editions based on usage and scale:

• DB2 Express-C – Free edition for learning and small apps
• DB2 Express – Entry-level production workloads
• DB2 Workgroup Server Edition
• DB2 Enterprise Server Edition
• DB2 Advanced Enterprise Server Edition
• DB2 for z/OS – Mainframe environments

3. What is a Tablespace in DB2?

A tablespace is a logical storage unit that holds database objects like tables and indexes. It acts as a link between physical storage and logical database objects.

Types of tablespaces:

• System Managed Space (SMS)
• Database Managed Space (DMS)
• Automatic Storage (recommended)

4. What is a Buffer Pool?

A buffer pool is a memory area used by DB2 to cache data pages read from disk. It improves performance by reducing disk I/O.

Advantages:

• Faster data access
• Reduced disk operations
• Better query performance

5. What is the difference between CHAR and VARCHAR?

6. What is a Cursor in DB2?

A cursor is used to retrieve and process rows one at a time from a result set in SQL, especially in embedded SQL or stored procedures.

Cursor lifecycle:

1. Declare
2. Open
3. Fetch
4. Close

7. What is a Stored Procedure?

A stored procedure is a precompiled SQL program stored in the database that can contain SQL statements, logic, and control structures.

Benefits:

• Improved performance
• Code reusability
• Enhanced security
• Reduced network traffic

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

9. What is an Index in DB2?

An index is a database object that improves the speed of data retrieval operations.

Types of indexes:

• Clustered index
• Non-clustered index
• Unique index
• Composite index

10. What is a Primary Key and Foreign Key?

• Primary Key: Uniquely identifies each row in a table and cannot contain NULLs.
• Foreign Key: Refers to a primary key in another table and enforces referential integrity.

11. What is Normalization?

Normalization is the process of organizing data to reduce redundancy and improve data integrity.

Normal Forms:

• 1NF – Atomic values
• 2NF – No partial dependency
• 3NF – No transitive dependency

12. What is Denormalization?

Denormalization is the process of adding redundancy to improve query performance, especially in read-heavy systems.

13. What is a View in DB2?

A view is a virtual table based on a SELECT query.

Advantages:

• Simplifies complex queries
• Enhances security
• Improves maintainability

14. What is a Deadlock in DB2?

A deadlock occurs when two or more transactions block each other, waiting for resources.

DB2 handles deadlocks by:

• Detecting automatically
• Rolling back one transaction

15. What is Locking in DB2?

Locking prevents concurrent users from accessing the same data in a conflicting way.

Types of locks:

• Row-level
• Page-level
• Table-level

16. What is Isolation Level in DB2?

Isolation levels control how data is accessed by concurrent transactions.

Types:

• Read Uncommitted (UR)
• Read Committed (CS)
• Repeatable Read (RS)
• Serializable (RR)

17. What is Explain Plan?

Explain Plan shows how DB2 executes an SQL query, including access paths and join methods.

Used for:

• Query optimization
• Performance tuning

18. What is RUNSTATS?

RUNSTATS collects statistics about database objects, helping the optimizer choose the best access path.

19. What is REORG in DB2?

REORG reorganizes tables and indexes to improve performance and reclaim space.

20. What is a Package in DB2?

A package is a compiled form of SQL statements used by applications, improving execution efficiency.

21. What is Bind in DB2?

BIND associates DB2 packages with application programs, enabling SQL execution.

22. What is DB2 Catalog?

The DB2 catalog is a set of system tables that store metadata about database objects.

23. What is the difference between INNER JOIN and OUTER JOIN?

• INNER JOIN returns matching rows
• OUTER JOIN returns matching rows plus unmatched rows

24. What is Partitioning in DB2?

Partitioning divides large tables into smaller, manageable pieces to improve performance and maintenance.

25. How do you improve DB2 query performance?

Best practices include:

• Use proper indexes
• Analyze Explain Plan
• Run RUNSTATS regularly
• Avoid SELECT *
• Optimize joins and subqueries
• Use appropriate isolation levels

Conclusion

IBM DB2 remains a critical enterprise database skill, especially in industries that demand high performance and reliability. Mastering these top 25 IBM DB2 developer interview questions will help you confidently tackle technical interviews and real-world DB2 challenges.

If you're a fresher or transitioning professional, focusing on SQL fundamentals, indexing strategies, and performance tuning concepts will significantly improve your DB2 career prospects.