The Top Oracle Database Developer Interview Questions and Answers

Landing a job as an Oracle Database Developer requires strong technical skills and in-depth knowledge of Oracle’s complex architecture The interview process will test your expertise through a series of tricky Oracle database questions Knowing what questions to expect and being prepared with strong answers can help you stand out from other candidates.

In this comprehensive guide we provide insider tips on how to ace the Oracle developer interview along with the top technical and behavioral questions you’re likely to encounter.

Why Oracle Database Developer Interviews Are Challenging

During the Oracle database developer interview, you can expect both technical queries focused on your hands-on skills as well as behavioral questions aimed at understanding your problem-solving abilities, communication skills, and your motivation for the role. Here are a few reasons these interviews can be tricky to crack:

• In-depth Technical Questions: Interviewers will ask probing technical questions to evaluate your real-world expertise with Oracle. They want specific examples of how you’ve used Oracle tools and features, not just theoretical knowledge. You need to demonstrate hands-on skills.

• Testing Your Problem-Solving Abilities: Oracle database management involves constantly troubleshooting issues and optimizing performance. Interviewers will present you with complex scenarios to assess analytical skills.

• Assessing Communication Skills: A major aspect of the role involves collaborating with teams and explaining technical concepts clearly. Interviewers look for strong verbal and written communication abilities.

• Gauging Your Passion: Working with Oracle requires continuous learning and staying updated on new developments. Interviewers look for genuine interest and enthusiasm for the role.

Thorough preparation focusing on these areas is key to clearing the Oracle database developer interview.

Top Technical Oracle Interview Questions and Answers

Let’s look at some of the most common technical Oracle interview questions you’re likely to face:

Q1: Explain normalization and its advantages in Oracle database design.

Normalization is the process of efficiently organizing data in a database to minimize redundancy and dependencies. Its key advantages include:

• Ensures data integrity and accuracy by eliminating inconsistent dependencies and anomalies.

• Improves query performance as fewer joins are required to retrieve data.

• Reduces storage overhead by eliminating redundant data.

• Simplifies maintenance by avoiding inconsistencies caused by database modifications.

• Enables easier expandability as tables can be altered without affecting other parts of the database.

Q2: How can you optimize a slow-running Oracle query?

Some techniques to optimize slow queries in Oracle include:

• Reviewing the query execution plan to identify bottlenecks like full table scans or missing indexes.

• Adding indexes on columns frequently used in JOIN and WHERE clauses.

• Tuning and rewriting SQL statements to improve suboptimal joins, functions, and subqueries.

• Using hints like FIRST_ROWS or PARALLEL to influence the optimizer’s execution plan.

• Partitioning large tables based on usage patterns.

• Caching frequently executed queries using Result Cache.

• Gathering optimizer statistics to help choose optimal execution plans.

Q3: What are the differences between clustered and non-clustered indexes?

The key differences are:

• Data Storage: Clustered indexes physically store table data in index order whereas non-clustered indexes only contain the index keys and row locators pointing to the actual data.

• Index Structure: Clustered indexes are more performance optimized as related data is stored in contiguous blocks. Non-clustered indexes have more overhead for random access.

• Number of Indexes: Only one clustered index can be created per table as the data can only be physically organized in one order. Many non-clustered indexes can be defined.

• Uniqueness: Clustered indexes automatically contain the uniqueness property on the indexed columns. Non-clustered indexes must specify the unique constraint explicitly.

Q4: How can you identify a SQL statement that is causing poor performance in Oracle?

The methods are:

• Reviewing Active Session History (ASH) reports to identify long running SQL.

• Generating ADDM reports to pinpoint high-load SQL.

• Tracing sessions using SQL Trace and TKPROF to capture problematic statements.

• Enabling automatic SQL Tuning Advisor to receive recommendations on tuning high-load SQL.

• Running manual explain plans on suspected SQL statements.

• Monitoring v$ views like v$sqlarea to find resource-intensive SQL.

Q5: What are the differences between TRUNCATE, DELETE and DROP statements in Oracle?

• TRUNCATE removes all data quickly by deallocating the data blocks used by the table. It cannot be rolled back and does not fire any DELETE triggers.

• DELETE removes data row-by-row which can be rolled back. It fires DELETE triggers for each row removal.

• DROP removes the entire table structure from the database and cannot be rolled back. Dependent objects like indexes are also removed.

Q6: How can you identify whether a SQL statement will use an index in Oracle?

Ways to verify if a statement will use index access include:

• Examining its execution plan for an access method of INDEX.

• Checking the cost and cardinality estimates in the plan. Lower estimates indicate index usage.

• Using hints like INDEX, USE_NL, or INDEX_ASC to enforce index usage.

• Reviewing the explain plan for the join method used. Access via INDEX indicates index use.

• Checking views like V$SQL_PLAN for objects like INDEX in the operations list.

Q7: What are the potential locking issues that can arise in Oracle databases?

Common locking issues include:

• Deadlocks where two transactions end up waiting for locks held by each other.

• Unindexed foreign key columns leading to excessive row-level locks.

• Frequent DML causing increased contention for table-level locks.

• Excessive locking due to poorly written queries using subqueries and temporary tables.

• Locks not being released after transaction completion due to coding errors.

• Running out of available locks due to high concurrency workloads.

Q8: How can you identify unused indexes in an Oracle database?

Methods to find unused indexes:

• Checking v$ object_usage view for indexes with 0 usage.

• Reviewing index monitoring reports for indexes not being accessed.

• Analyzing index statistics to identify indexes with low cardinality.

• Running Oracle’s Index Advisor to get index optimization recommendations.

• Enabling monitoring of index usage at the session level.

• Tracing SQL statements to verify if indexes are being used.

• Queries joining from unused indexes can indicate their non-utilization.

Q9: You face frequent “snapshot too old” errors in Oracle. How would you troubleshoot this?

I would troubleshoot it by:

• Increasing the undo tablespace to prevent overwriting of unexpired undo data.

• Reducing frequent large transactions holding long locks.

• Decreasing undo retention period if acceptable for the application.

• Separating undo tablespaces to avoid single hotspot.

• Enabling Flashback Query where possible instead of consistent reads.

• Examining straddling snapshots caused by DDL/DML concurrent activity.

• Analyzing transactions using undo data older than recycle time.

Q10: How can you identify performance issues with Oracle database triggers?

Ways to analyze trigger performance:

• Check v$ views for trigger execution metrics like waits and CPU usage.

• Compare AWR reports before and after trigger creation to identify impact.

• Use client-side tracing to capture trigger execution time per operation.

• Monitor locks and latches during trigger execution.

• Check for recursion errors which indicate inefficient logic.

• Utilize bulk triggers where possible to reduce overhead.

• Ensure minimal logging and use of temporary tables within trigger logic.

Top Oracle Interview Questions on PL/SQL

PL/SQL is a fundamental skill for Oracle database developers. Here are some key PL/SQL interview questions:

Q1: Explain PL/SQL collections and their usage.

PL/SQL collections are complex data types that allow storing multiple elements of the same data type. The three types are nested tables, varrays, and associative arrays. Their key benefits are:

• Improve performance by reducing context switching between PL/SQL and SQL engines.

• Simplify coding by manipulating multiple elements in one go.

• Allow passing data between subprograms easily.

• Help in memory management within PL/SQL blocks.

• Enable handling query results efficiently.

I have used them for use cases like holding high volume query results and passing them within nested subprograms.

Q2: How can you do exception handling in PL/SQL?

Exception handling in PL/SQL can be done using:

• Predefined exceptions for common Oracle errors using EXCEPTION_INIT pragma.

• Programmer-defined exceptions with RAISE_APPLICATION_ERROR.

• Implicit exceptions for all other errors using EXCEPTION block.

• WHEN OTHERS exception handler to catch all unhandled exceptions.