DB2 Interview Questions and Answers for 10 years experience

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100 DB2 Interview Questions and Answers

  1. What are the different types of joins in DB2? Explain with examples.

    • 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, and matching rows from the right; NULLs if no match), RIGHT (OUTER) JOIN (opposite of LEFT JOIN), and FULL (OUTER) JOIN (returns all rows from both tables, NULLs where there's no match). Example: An INNER JOIN between Employees and Departments tables would only return employees who belong to an existing department. A LEFT JOIN would return all employees, even if their department is missing from the Departments table.

  2. Explain the concept of indexes in DB2 and their different types.

    • Answer: Indexes are data structures that improve the speed of data retrieval operations in DB2. They work similarly to an index in a book. Types include B-tree indexes (most common, efficient for range searches and equality searches), unique indexes (ensure uniqueness of a column or set of columns), clustered indexes (physically order data rows based on index key), and function-based indexes (created on the result of a function applied to a column).

  3. 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 to handle them include: proper locking strategies (using shorter locks, avoiding unnecessary locking), using short transactions, monitoring deadlock occurrences via DB2 tools (to identify problematic queries or processes), and configuring appropriate deadlock timeout values.

  4. What is the difference between COMMIT and ROLLBACK?

    • Answer: COMMIT permanently saves changes made during a transaction. ROLLBACK undoes the changes made during a transaction, restoring the database to its state before the transaction began. COMMIT ensures data integrity, while ROLLBACK provides a mechanism to recover from errors or unintentional changes.

  5. Explain the various isolation levels in DB2.

    • Answer: Isolation levels control the degree to which transactions are isolated from each other. They range from low isolation (allowing more concurrency but potential for anomalies like dirty reads) to high isolation (reducing concurrency but preventing anomalies). Levels include: Uncommitted read, Committed read, Repeatable read, Serializable.

  6. How do you optimize query performance in DB2?

    • Answer: Query optimization involves several techniques: using appropriate indexes, writing efficient SQL (avoiding full table scans), analyzing execution plans (using DB2's explain facilities), using hints to guide the optimizer, partitioning large tables, and normalizing the database design.

  7. What are stored procedures in DB2 and their advantages?

    • Answer: Stored procedures are pre-compiled SQL code stored in the database. Advantages include: improved performance (due to pre-compilation), enhanced security (can control access to database objects), modularity (breaking down complex tasks into smaller units), and code reusability.

  8. Explain the concept of triggers in DB2.

    • Answer: Triggers are procedural code automatically executed in response to certain events on a particular table (like INSERT, UPDATE, DELETE). They're useful for implementing business rules, auditing changes, and maintaining data integrity. For example, a trigger can enforce a constraint that prevents deleting a customer if they have outstanding orders.

  9. Describe different types of DB2 backup and recovery strategies.

    • Answer: DB2 offers various backup methods: full backups (copying the entire database), incremental backups (copying only changes since the last backup), and differential backups (copying changes since the last full backup). Recovery strategies involve restoring from a full backup and applying incremental backups or using logs for point-in-time recovery.

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