Top 10 advanced-level questions that are commonly asked for an experienced Oracle PL/SQL Developer. These questions are focused on advanced features, optimization, problem-solving, and real-life scenarios.
- What is the difference between ROWID and ROWNUM, and how can they be used in optimizing PL/SQL queries?
Explanation: ROWID is a unique identifier for each row in the database, pointing to its physical location, while ROWNUM is a sequential number assigned to each row in a result set. Discuss scenarios where each can be useful, particularly for pagination or selective row processing, and how they may impact query optimization.
- How do you implement exception handling in PL/SQL to ensure that errors are logged without interrupting transaction flow?
Explanation: Demonstrate advanced exception handling using autonomous transactions to log errors with RAISE_APPLICATION_ERROR or PRAGMA EXCEPTION_INIT, and discuss how this approach ensures continuity without rolling back the main transaction.
- Explain the use and performance benefits of BULK COLLECT and FORALL. What are some limitations you need to consider?
Explanation: Describe how BULK COLLECT and FORALL are used to handle large data sets more efficiently by reducing context switches, and explain their limitations, such as handling exceptions in FORALL and managing memory consumption in large collections.
- What are materialized views, and how can they be optimized in a high-transaction environment with refresh mechanisms like FAST, COMPLETE, and ON DEMAND?
Explanation: Discuss the different refresh methods for materialized views and how to use them effectively, particularly in scenarios where data must be periodically synchronized but performance is a critical consideration.
- Describe how you would use dynamic SQL in PL/SQL and the potential security risks associated with it. How can you mitigate these risks?
Explanation: Explain the purpose of dynamic SQL with EXECUTE IMMEDIATE and DBMS_SQL, particularly for flexible, parameterized queries. Address security risks such as SQL injection and how to mitigate them by using bind variables.
- What are REF CURSORs, and how would you use them for passing query results between PL/SQL programs and applications?
Explanation: Provide an example of using REF CURSORs to return result sets to front-end applications, discuss performance considerations, and highlight scenarios where REF CURSORs can enhance application flexibility.
- How would you use indexing strategies and partitioning to improve query performance on a large, high-volume table?
Explanation: Describe types of indexes (B-tree, bitmap, composite) and when to use each. Explain how partitioning (range, list, hash) can optimize data retrieval and performance in high-volume databases, particularly in scenarios such as telecom call data records.
- Explain row-level and table-level locking in Oracle. How would you detect and resolve a deadlock scenario in PL/SQL?
Explanation: Detail the differences between row-level and table-level locking, how Oracle handles concurrency, and techniques for avoiding deadlocks. Include methods for detecting deadlocks using V$LOCK views and resolving them through careful transaction management.
- What are autonomous transactions, and when would you use them in PL/SQL? Give an example.
Explanation: Explain the concept of autonomous transactions, their uses (such as logging in exception handling), and how to create one with PRAGMA AUTONOMOUS_TRANSACTION. Highlight scenarios where they’re useful without impacting the parent transaction.
- How would you approach troubleshooting a poorly performing PL/SQL procedure in production? What tools and techniques would you use?
Explanation: Describe your approach, including using EXPLAIN PLAN, SQL trace, and DBMS_PROFILER to analyze and pinpoint performance bottlenecks. Explain how you would optimize SQL queries, restructure logic, and tune PL/SQL code based on profiling results.
These questions are aimed at evaluating your depth of knowledge, your ability to optimize and troubleshoot in complex situations, and your awareness of best practices in security and performance. Preparing with examples and real-life scenarios where you applied these techniques will give you a strong foundation for advanced-level PL/SQL interviews.
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