DB2 is a database management system created by IBM in the early 1980s. It started as a project to support SQL and became one of the first commercial relational databases. Designed to handle large volumes of data, DB2 is widely used in banking, insurance, and enterprise applications. It helps store, manage, and retrieve data efficiently. Many roles like database administrator, data analyst, and backend developer need DB2 skills. This blog covers 25+ commonly asked DB2 interview questions and answers to help you get ready for your next interview.
DB2 Interview Questions for Freshers
Here are some commonly asked DB2 interview questions and answers to help freshers prepare.
- What is DB2 and how do you use it?
DB2 is a relational database management system (RDBMS) developed by IBM. It helps manage structured data and supports SQL. DB2 is widely used in enterprise systems, especially on mainframes and Linux. I use it to create, store, and query data in tables using SQL.
- What are the common data types in DB2?
DB2 supports several data types like INTEGER, SMALLINT, BIGINT, CHAR, VARCHAR, DATE, TIME, FLOAT, and DECIMAL. VARCHAR adjusts to the actual string length, while CHAR is fixed.
- What is SQLCA and why is it important?
SQLCA stands for SQL Communication Area. It is a structure used in host languages like COBOL or C to receive the status of executed SQL statements. It includes important fields like SQLCODE, which shows if the query ran successfully or failed.
- What is the role of a buffer pool in DB2?
A buffer pool is memory allocated to cache table and index pages. It reduces disk I/O by keeping frequently accessed data in memory. This speeds up query performance.
- How are transactions managed in DB2 using COMMIT and ROLLBACK?
COMMIT is used to save all changes made during a transaction. ROLLBACK cancels those changes if something goes wrong. These help keep data consistent and avoid partial updates.
- What are the DB2 isolation levels and their differences?
DB2 supports four isolation levels:
- UR (Uncommitted Read)
- CS (Cursor Stability)
- RS (Read Stability)
- RR (Repeatable Read)
UR allows dirty reads. CS locks only the current row being read. RS avoids non-repeatable reads. RR provides the highest consistency but may slow performance due to locking.
DB2 Interview Questions for Experienced
These DB2 interview questions and answers are commonly asked to experienced professionals.
- How do you use the EXPLAIN tool to analyze a DB2 query’s execution plan?
I run the EXPLAIN command before executing a SQL query. It writes query execution details into the PLAN_TABLE. From there, I review how DB2 plans to access data – whether it uses an index, scans a table, or joins tables efficiently. This helps me spot costly operations and fix performance issues before they hit production.
- What are DBRM and the BIND process?
A DBRM (Database Request Module) is created during precompilation. It contains all SQL from the source code. The BIND process then converts the DBRM into a package stored in the DB2 catalog. BIND lets DB2 check access rights, optimize queries, and set runtime options.
- How do you handle deadlocks in DB2?
Deadlocks happen when two applications wait on each other’s resources. DB2 automatically picks a victim to roll back. But I don’t wait for that.
I reduce deadlocks by keeping transactions short, accessing tables in the same order, and using proper isolation levels. I also monitor for deadlock events using tools like db2diag.log and snapshot reports.
- How do you back up and restore a DB2 database?
I use db2 backup db <dbname> for full offline or online backups. I schedule incremental backups for large systems. To restore, I run db2 restore db <dbname> and, if needed, roll forward using transaction logs. This lets me recover to a specific point in time.
- What is the difference between static and dynamic SQL in DB2?
Static SQL is compiled at bind time. It is fast and stable. Dynamic SQL is compiled at runtime, useful for flexible queries. Static is better for performance, dynamic for flexibility.
- What are DB2 LUW and DB2 for z/OS, and how do they differ?
DB2 LUW (Linux, Unix, Windows) runs on distributed systems. DB2 for z/OS runs on IBM mainframes. LUW is used in modern enterprise apps. z/OS is chosen for high availability, transaction-heavy environments like banks.
Scenario Based DB2 Interview Questions
Let’s go through some DB2 scenario based interview questions for experienced and freshers.
- How would you diagnose a slow-running DB2 query and improve its performance?
First, I run the EXPLAIN command to check the access plan. I see if it’s using a full table scan instead of an index. Then I check table statistics – outdated stats often cause bad plans.
I also look at buffer pool usage, lock waits, and sort overflows. Based on what I find, I may rewrite the query, create or fix indexes, or run RUNSTATS.
- Describe a time you had to resolve frequent deadlocks in DB2.
I once worked on a system with random deadlocks during peak hours. I analyzed lock events using db2diag.log and snapshots. I found that two programs were updating the same tables in different orders. I changed the access order and reduced the transaction size. After that, the deadlocks stopped.
- How would you migrate large volumes of data between DB2 databases with minimal downtime?
I use the DB2 EXPORT and LOAD utilities or db2move. For minimal downtime, I export during low-traffic hours, then sync delta data using triggers or log shipping. I also test the whole process in a staging environment before the final cutover.
- Tell me how you would configure a high-availability setup for DB2 (e.g., HADR).
To set up HADR, I configure the primary and standby databases with log shipping enabled. I set up the HADR pair with the correct sync mode – usually “near sync” or “async” for better performance. Then I automate failover using TSA or Pacemaker.
DB2 Queries Interview Questions
Now, we will cover DB2 queries for interview that test your ability to write and understand SQL statements commonly used in DB2 environments.
- What types of joins does DB2 support and when might you use each?
DB2 supports INNER JOIN, LEFT OUTER JOIN, RIGHT OUTER JOIN, FULL OUTER JOIN, and CROSS JOIN.
- INNER JOIN returns rows where both tables have matching values.
- LEFT JOIN returns all rows from the left table and matched rows from the right.
- RIGHT JOIN does the opposite.
- FULL JOIN returns all matching and non-matching rows from both tables.
- CROSS JOIN creates a Cartesian product. Use it when every combination matters.
- What is a clustering index in DB2?
A clustering index arranges rows in the physical table to match the index order. It improves query performance when data is accessed sequentially. Only one clustering index is allowed per table. It speeds up range scans and helps with table reorgs.
- How is UNION different from UNION ALL in DB2?
UNION combines results from two queries and removes duplicates. UNION ALL includes duplicates. Use UNION when you need unique rows. Use UNION ALL when every record matters and performance is more important than filtering.
- What is the difference between DELETE FROM and DROP TABLE in DB2?
DELETE FROM removes all rows but keeps the table structure. It can be rolled back. DROP TABLE removes the entire table and its definition permanently. It can’t be undone without a backup. Use DELETE when you will reuse the table.
DB2 DBA Interview Questions
Here are some DB2 DBA interview questions for experienced and freshers that focus on database administration tasks.
- What are tablespaces in DB2 and why are they used?
Tablespaces are logical storage units in DB2. They group related tables and indexes to control how data is stored. By using tablespaces, DBAs can isolate data, manage performance, and organize backups more easily.
- What is RUNSTATS and when should it be run?
RUNSTATS collects statistics on tables and indexes. These stats help the optimizer choose efficient access paths. I usually run it after bulk inserts, deletes, or updates. It is also part of regular DB2 maintenance.
- How do you manage tablespace volumes or move them between storage groups?
To move a tablespace, I use ALTER STOGROUP to add the new volume and delete the old one. Then I run REORG TABLESPACE to move the data physically. This method avoids dropping and recreating objects.
- What types of locks does DB2 support and what are their purposes?
DB2 supports several locks: table, row, page, and tablespace locks. It uses intent locks like IS, IX, and SIX to show the type of access needed. These locks control concurrency and protect data from conflicts during transactions.
DB2 COBOL Interview Questions
These are COBOL DB2 interview questions for experienced professionals working with legacy systems and mainframe applications that use both COBOL and DB2.
- What is DCLGEN in DB2 for COBOL programs?
DCLGEN stands for Declarations Generator. It creates the table declaration and host variable structures for COBOL programs. This saves time and avoids manual errors. I use it to sync the COBOL copybook with the DB2 table structure.
- Where are SQL statements coded in a COBOL-DB2 program?
In a COBOL-DB2 program, SQL statements are coded in Area B of the Procedure Division. This is where executable instructions are written. DECLAREs and other SQL precompiler instructions are placed before the main logic begins.
- What is SQLCA and how many can you have in a COBOL program?
SQLCA stands for SQL Communication Area. It is a structure that stores information after every SQL operation. It includes SQLCODE and SQLSTATE. Only one SQLCA is needed in most COBOL programs. FORTRAN allows more than one, but COBOL doesn’t require it.
- What is the difference between static and dynamic SQL in a COBOL-DB2 context?
Static SQL is embedded in the program and compiled during BIND. It is faster and used for fixed queries. Dynamic SQL is built and executed at runtime. It is useful when query structure depends on user input or external conditions.
DB2 Questions for Mainframe Interview
Here are Mainframe DB2 scenario based interview questions for experienced candidates to help you tackle real situations in mainframe environments.
- What levels of locking does DB2 support on the mainframe?
DB2 on mainframe supports multiple locking levels – table, tablespace, page, and row-level. Page and row-level locks allow more concurrency. Lock size can be set during tablespace creation or controlled dynamically. It helps balance performance and data integrity.
- What is the difference between static and dynamic SQL in DB2 mainframe environments?
Static SQL is precompiled and bound before the program runs. It is used in most COBOL-DB2 batch or online programs. It gives better performance. Dynamic SQL is built and executed at runtime, usually with EXECUTE IMMEDIATE or PREPARE and EXECUTE. It is more flexible but slightly slower.
- How does DB2 handle recovery and rollbacks after an unexpected abend (crash)?
If a program abends, DB2 automatically rolls back all uncommitted changes. It uses the transaction log to undo changes made since the last COMMIT. This keeps the data consistent even after failure. Recovery logs are key.
- How can you run DB2 queries in batch mode using JCL or REXX?
In JCL, you can use the IKJEFT01 utility to run DB2 commands or call programs that contain SQL. You pass queries via SYSIN. In REXX, you use the DSNREXX interface to connect to DB2 and run SQL statements within scripts.
How to Prepare for DB2 Interview?
Preparing for a DB2 interview takes more than memorizing questions. You need hands-on clarity too. So, follow these tips to prepare:
- Learn DB2 basics like tablespaces, indexes, and locking
- Practice SQL queries on real DB2 tables
- Understand how buffer pools and RUNSTATS work
- Read recent performance tuning scenarios
- Review DB2 with COBOL if applying for mainframe roles
- Check logs, EXPLAIN plans, and rollback handling
- Do mock interviews to get used to technical questions
Wrapping Up
With these 25+ DB2 interview questions and answers, you now have a strong base to prepare well. Focus on real examples and practice regularly to stay confident.
Looking for DB2 job roles or other IT jobs? Find top openings now on Hirist.
FAQs
For professionals with 10+ years of DB2 experience, interviews often focus on performance tuning, disaster recovery, and architecture-level planning. Here are the common questions:
How do you approach performance tuning in a high-volume DB2 environment?
What is your process for designing a DB2 backup and recovery strategy for enterprise systems?
How do you manage DB2 version upgrades with minimal downtime?
Explain the use of data partitioning and how it impacts query performance.
What are your best practices for DB2 buffer pool tuning?
Capgemini interviews often include real scenarios, tuning strategies, and integration with enterprise systems. Here are the commonly asked questions:
How do you perform online REORG in DB2 without impacting active users?
What is the use of COPY PENDING status and how do you resolve it?
How do you manage DB2 subsystem parameters for performance?
Explain how DB2 interacts with CICS in a mainframe environment.
What steps do you follow for DB2 disaster recovery in a multi-node setup?
They can be challenging if you are not familiar with real-time DB2 administration tasks. Focused hands-on experience makes them easier to tackle. These common questions are often asked in interviews:
How do you monitor and manage DB2 transaction logs?
What is the use of DSNZPARM in DB2?
How do you handle catalog and directory corruption in DB2?
What steps do you follow to resize buffer pools?
How do you manage schema changes in a live DB2 environment?
According to AmbitionBox, the average salary at IBM ranges from ₹9 Lakhs to ₹21 Lakhs per year depending on experience. The average annual salary is 15 Lakhs. The monthly in-hand take-home pay for IBM DB2 DBAs in Gurgaon is reported between ₹1 Lakh to ₹1.1 Lakh.
IBM DB2 Database Administrator Salary Overview (India, 2025)
| Metric | Value |
|---|---|
| Annual salary range | ₹9 Lakhs – ₹21 Lakhs |
| Avg. annual salary | ₹15 Lakhs |
| Monthly in-hand salary | ₹1 Lakh – ₹1.1 Lakh |
| Experience range | 2-10 years |
Salary based on experience
| Experience | Average Annual Salary |
|---|---|
| 2 years | ₹9.0 Lakhs per year |
| 3 years | ₹10.5 Lakhs per year |
| 4 years | ₹12.0 Lakhs per year |
| 5 years | ₹13.5 Lakhs per year |
Salary at top IT companies
| Company | Average Annual Salary |
|---|---|
| HCLTech | ₹13.5 Lakhs per year |
| Accenture | ₹12.0 Lakhs per year |
| HCL Group | ₹10.9 Lakhs per year |
| Cognizant | ₹10.5 Lakhs per year |
| Infosys | ₹9.9 Lakhs per year |
Most companies conduct 2–4 rounds:
Round 1: Technical screening (SQL, DB2 basics)
Round 2: Scenario-based DBA questions
Round 3: Managerial or system design round
Final: HR discussion
Companies like IBM, Capgemini, TCS, Infosys, HCLTech, and Cognizant frequently hire for DB2 DBA positions across India, especially for mainframe and enterprise system projects.
