DB2 Interview Questions and Answers for experienced

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100 DB2 Interview Questions and Answers

  1. What is DB2?

    • Answer: DB2 is a relational database management system (RDBMS) developed by IBM. It's known for its robustness, scalability, and support for large transactional workloads. It's available in various editions, including DB2 for LUW (Linux, UNIX, and Windows), DB2 for z/OS (mainframes), and DB2 for i (IBM i systems).

  2. Explain the different types of DB2 indexes.

    • Answer: DB2 offers several index types, including B-tree indexes (the most common, used for efficient searching, sorting, and joining), unique indexes (ensure uniqueness of indexed columns), clustered indexes (physically order data based on index), and function-based indexes (indexes on expressions or functions applied to columns). Each has its strengths and weaknesses depending on query patterns and data characteristics.

  3. What are the advantages of using stored procedures in DB2?

    • Answer: Stored procedures offer several advantages: improved performance due to pre-compilation, enhanced security by encapsulating database logic, code reusability, reduced network traffic (since less data needs to be transmitted), and simplified application development.

  4. How do you handle deadlocks in DB2?

    • Answer: Deadlocks occur when two or more transactions are blocked indefinitely, waiting for each other to release locks. Strategies for handling deadlocks include: using shorter transactions, careful ordering of locks, setting appropriate timeouts, and using DB2's deadlock detection and resolution mechanisms which usually involve rolling back one of the conflicting transactions.

  5. Explain the concept of ACID properties in DB2.

    • Answer: ACID properties ensure data integrity and consistency in database transactions: Atomicity (all changes happen or none), Consistency (data moves from one valid state to another), Isolation (transactions are independent), and Durability (committed changes survive failures).

  6. What are different types of joins in DB2?

    • Answer: DB2 supports various join types: INNER JOIN (returns rows only when there's a match in both tables), LEFT (OUTER) JOIN (returns all rows from the left table, matching rows from the right table, and NULLs where there's no match), RIGHT (OUTER) JOIN (similar to LEFT JOIN but with roles reversed), FULL (OUTER) JOIN (returns all rows from both tables), and CROSS JOIN (returns the Cartesian product of both tables).

  7. How do you optimize query performance in DB2?

    • Answer: Query optimization involves several techniques: creating appropriate indexes, using efficient joins, optimizing WHERE clauses, avoiding SELECT *, using bind variables, analyzing execution plans with EXPLAIN, and ensuring proper database statistics are updated.

  8. Explain the different levels of isolation in DB2.

    • Answer: DB2's isolation levels control concurrency and how transactions interact: Read Uncommitted (allows dirty reads), Read Committed (prevents dirty reads), Repeatable Read (prevents dirty and non-repeatable reads), and Serializable (prevents dirty, non-repeatable, and phantom reads).

  9. What is a cursor in DB2?

    • Answer: A cursor is a database object that allows you to process the result set of a query row by row, rather than all at once. This is crucial for applications that need to process large result sets or perform actions based on individual rows.

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