Top Oracle Interview Questions and Answers [2025]

CTA

• What is an Oracle?
• Recruitment Process of Oracle
• Oracle Interview Question
  • Basic Interview Questions for Beginners
  • Intermediate Interview Questions
  • Advanced Interview Questions for Experienced
  • Scenario-Based Interview Questions
  • Technical Interview Questions
  • Behavioral Oracle Interview Questions
• Conclusion

What is Oracle?

Recruitment Process of Oracle

1. Application: Upload your resume through Oracle’s career portal or via employee referrals.
2. Online Assessment: Includes coding questions (Java/SQL), aptitude tests, and problem-solving scenarios.
3. Technical Rounds: Focus on SQL/PLSQL coding, database design principles, and Oracle Cloud Infrastructure (OCI)-related questions.
4. Behavioural Round: STAR-method questions assessing teamwork, adaptability, and problem-solving capabilities.
5. HR Discussion: Covers salary negotiation, role expectations, and the onboarding process.

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Oracle Interview Questions

Basic Interview Questions for Beginners

Q1. What is Oracle Database?

Oracle Database is a relational database management system (RDBMS) developed by Oracle Corporation. It is designed to efficiently store, manage, and retrieve large volumes of structured data and supports SQL for querying.

Q2. What is a relational database management system (RDBMS)?

A Relational Database Management System is application software designed to manage and manipulate data structured in rows and columns across multiple tables. RDBMSs inherently have data integrity and perform database functionality such as inserting, updating, deleting, and querying data, most often through a query language, Structured Query Language (SQL).

Q3. What are the various types of Oracle database objects? 

Some common types of Oracle database objects are tables, views, indexes, sequences, synonyms, procedures, functions, packages, and triggers.

Q4. What is a table in Oracle? 

A table is an Oracle object, which is used to store data in rows and columns, where each row represents a record and each column represents a field of the data.

Q5. What is the difference between VARCHAR and VARCHAR2 in Oracle? 

Oracle has reserved the VARCHAR datatype for future use. VARCHAR behaves like VARCHAR2 in current releases of the Oracle database; however, in future releases, VARCHAR may behave differently than VARCHAR2. 

Q6. What is a primary key? 

A primary key is a column or grouping of columns that uniquely identifies each row in the table. A primary key cannot include any null values but can have unique values.

Q7. What is a foreign key in Oracle? 

A foreign key is a column that defines the relationship between two tables. It refers to the primary key in another table. The foreign key guarantees referential integrity.

Q8. What is a view? How does it differ from a table? 

A view is a ‘virtual’ table based upon the result of a SQL query. A view is not a table because it does not store the data physically. It presents the data that is stored in one or more tables. 

Q9. What are the physical components of the Oracle Database?

Five physical components are there in the Oracle Database:

1. Parameter files
2. Data files
3. Control files
4. Redo log files
5. Password files

Q10. What are the constraints in Oracle? Name some. 

Constraints are rules that define certain actions enforced on the data in the tables. Some types include  

1. NOT NULL  
2. UNIQUE  
3. PRIMARY KEY  
4. FOREIGN KEY  
5. CHECK

Q11. What is the difference between DELETE, TRUNCATE, and DROP?

• DELETE: Removes specific rows based on a condition and can be rolled back.
• TRUNCATE: Removes all rows faster than DELETE; cannot be rolled back.
• DROP: Removes the table structure and data permanently. 

Q12. What is an index in Oracle, and why is it used?

An index is a database object that improves the speed of data retrieval. It works like a pointer to data in a table, reducing the need to scan an entire table.

Q13. What are the different types of joins in Oracle SQL?

There are different types of joins in Oracle SQL.

1. INNER JOIN: Returns rows that have matching values in both tables.
2. LEFT JOIN: Returns all rows from the left table and matching rows from the right.
3. RIGHT JOIN: Returns all rows from the right table and matching rows from the left.
4. FULL OUTER JOIN: Returns all rows when there is a match in one of the tables.
5. CrossJOIN: Returns the Cartesian product of both tables.

Q14. What is the difference between a view and a materialised view in Oracle? 

A view is a virtual table based on a SQL query. It does not contain any data. A materialised view, on the other hand, stores the result of a query physically so that the data can be refreshed periodically.

Intermediate Interview Questions

Q15. Explain an Oracle tablespace.

A tablespace is a logical storage unit within an Oracle database. An Oracle tablespace is made up of one or more datafiles. This provides storage allocations for schema objects, such as tables and indexes.

Q16. What are the different types of indexes in Oracle?

Examples include B-tree index, Bitmap index, Unique index, Composite index, and Function-based index.

Q17. What is the difference between TRUNCATE and DELETE in Oracle?

DELETE is DML, can be rolled back, and fires triggers, whereas TRUNCATE is DDL, cannot be rolled back, and does not fire triggers.

Q18. Explain Oracle architecture components.

Oracle architecture components include the Oracle Instance with the System Global Area (SGA) plus background processes. The database is composed of the datafiles, redo log files, control files, and user processes.

Q19. What are sequences in Oracle? When are they used?

In Oracle, a sequence is a database object used to generate unique numbers automatically, often for primary key values. It helps avoid locking issues by generating IDs without depending on table data. Sequences are commonly used in multi-user environments to ensure fast and safe ID generation.

Q20. What is Oracle Data Pump, and how does it differ from EXP/IMP?

Oracle Data Pump (using expdp and impdp) is a high-speed utility for exporting and importing database objects. It’s faster than the older EXP/IMP, supports parallel execution, better filtering, and direct path loading, making it the preferred and more efficient method for data movement.

Q21. How does Oracle manage locking and concurrency? 

Oracle uses Multi-Version Concurrency Control (MVCC) to ensure that users can access consistent data without waiting. It manages locking at the row level, allowing multiple users to read and write simultaneously while preventing conflicts and maintaining data integrity.

Q22. What is the difference between %TYPE and %ROWTYPE in PL/SQL? 

%TYPE is used to declare a variable with the same data type as a specific column, while %ROWTYPE lets you declare a record with the same structure as a row in a table or cursor, including all its columns and their types.

Q23. Discuss the RANK() and DENSE_RANK() functions. 

Both are analytic functions in SQL that are used to rank rows based on a specific column. RANK() assigns the same rank to tied values but skips the next ranks, causing gaps. DENSE_RANK() also gives the same rank to ties but continues with the next number, so no gaps appear in the ranking.

Q24. What is a Dynamic SQL in Oracle?

Dynamic SQL is the ability to dynamically construct and execute SQL statements at runtime. Dynamic SQL is used when the precise SQL statement is not known until the time of execution. Dynamic SQL is executed using the EXECUTE IMMEDIATE statement or by using the DBMS_SQL package.

Advanced Interview Questions for Experienced

Q25. How does BULK COLLECT improve performance?

BULK COLLECT allows the program to grab multiple rows at once using only a single context switch from SQL to PL/SQL engine, which is extremely valuable when fetching large quantities of data.

Q26. What is FORALL in PL/SQL?

FORALL is a function to streamline context switching when performing DML operations within a loop. FORALL works with collections and performs DML operations in bulk to improve performance while using DML in a loop.

Q27. Define the term Autonomous Transactions.

An autonomous transaction is an independent transaction initiated by another transaction. Autonomous transactions can independently commit or roll back, and they do not influence the main (parent) transaction. Autonomous transactions are declared using the PRAGMA AUTONOMOUS_TRANSACTION command and are useful when logging or auditing operations must be committed independently. 

Q28. How will you handle exceptions in PL/SQL?

In PL/SQL, you could handle exceptions using the EXCEPTION block. Oracle has predefined exceptions like NO_DATA_FOUND, and user-defined exceptions can be declared and raised, which is done by using the RAISE command. 

Q29. What do you use the DBMS_STATS package for? 

The DBMS_STATS package is used to collect and manage statistics for the cost-based optimiser to make informed decisions about the most efficient way to execute a query. The better the data statistics, the better the execution plans will be generated for a particular SQL query. 

Q30 . What are Global Temporary Tables (GTT)?

Global Temporary Tables (GTT) store data that is session-private, which will go away when the session ends or the transaction ends. They are commonly used for storing intermediate results temporarily in the GTT. GTTs can be defined with ON COMMIT DELETE ROWS (transaction-level) or ON COMMIT PRESERVE ROWS (session-level). 

Q31. How do you avoid deadlocks in Oracle?

Here are some best practices to prevent deadlocks in Oracle databases: 

• Access your tables in a consistent order across all transactions.
• Keep your transactions short whenever possible and commit as early as feasible.
• Have proper locking discipline on your part.
• Avoid long-running transactions and try not to just delay committing.

Q32. What is a REF CURSOR, and when would you use it?

A REF CURSOR is a pointer to a query result set that allows dynamic and flexible data retrieval. It’s used when the query structure isn’t fixed or when passing result sets between PL/SQL blocks and external applications like Java or Python.

Q33. How are Analytical Functions different from Aggregate Functions?

For example, analytical functions (RANK(), LEAD(), LAG()) compute values over a given window of rows but do not collapse the result set. Aggregate functions (SUM(), AVG(), etc.) return a single value for each group of records.

Q34. What is Oracle Partitioning, and what are the benefits?

Partitioning is the process of breaking a table into smaller, more manageable pieces called partitions. Partitioning can improve performance for queries, manageability, and maintenance when dealing with larger amounts of data.

Q35. How do you tune a slow-performance SQL query in Oracle?

The tuning process includes reviewing execution plans, checking statistics with DBMS_STATS, and using appropriate indexes. It also involves avoiding full table scans and rewriting or restructuring queries to become more efficient by changing the types of joins.

Q36. What is the difference between hot backup and cold backup in Oracle?

A hot backup is done while the database is running in ARCHIVELOG mode, which continuously allows access. A cold backup is done while the database is stopped and allows the database to be in a consistent state.

Q37. Describe Oracle Data Guard and its various types.

Oracle Data Guard provides data protection and disaster recovery services by using both primary and standby databases. The standby databases are classified into Physical standby, Logical standby, and Snapshot standby.

Q38. What are AWR, ASH, and ADDM reports?

• AWR (Automatic Workload Repository) gathers data about the performance of a database.
• ASH (Active Session History) tracks database performance but only for active sessions.
• ADDM (Automatic Database Diagnostic Monitor) uses data from AWR to determine performance issues.

Q39. How do you troubleshoot locking and blocking problems?

To identify blocking sessions, look in v$session, v$lock, or you can use the various Enterprise Manager tools. To resolve blocking, you may need to kill sessions, change your transaction structure, or implement some scheme around locking.

Q40. How do you monitor and tune memory in Oracle?

Auto memory management is useful, but you can also look at SGA and PGA to understand allocation and memory usage by looking at v$SGA_DYNAMIC_COMPONENTS and v$PGA_TARGET_ADVICE. You may also want to tune MEMORY_TARGET and SGA_TARGET.

Q41. What is your strategy for database migration?

Migration is a matter of planning and using tools like Data Pump (expdp/impdp), RMAN, or GoldenGate to minimise downtime. Good testing and rollback protocols should be a part of the process before rolling out into production.

Q42. How do you implement security on an Oracle database?

Implement the least privilege principle using roles, user profiles, auditing (either with the AUDIT command or the Unified Audit Trail), and encryption (TDE). Also, ensure security on the network layer (Oracle Net Services).

Q43. What are bind variables, and why are they important?

Bind variables help prevent SQL injection and allow for improved performance by reusing SQL statements. They avoid hard parsing by allowing the optimised cache execution plans.

Q44. What is the difference between NOLOGGING and LOGGING options in Oracle?

NOLOGGING reduces the amount of redo logs created, which is helpful for bulk insert statements. But NOLOGGING means recovery could lead to data loss. LOGGING writes to the redo logs so that recovery is always possible.

Q45. How do you use Oracle's Resource Manager?

Oracle resource manager allows you to prioritise CPU and I/O resources among sessions. Resource plans are used to manage resources so that runaway queries cannot consume too many of the system resources.

Scenario-Based Interview Questions

Q46. Scenario: A critical query is running incredibly slowly in production. How would you troubleshoot?

• My first step is to capture the execution plan using EXPLAIN PLAN or DBMS_XPLAN.DISPLAY_CURSOR.
• Next, I will check the statistics for the tables used using DBMS_STATS.
• Then, I will look at AWR/ASH reports to get a sense of system performance.
• After I have checked all of that, I may consider checking indexes and rewriting the query or using hints.
• If things are still not performant, I will look into contention or locks on resources.

Q47. Scenario: A user is complaining that they can not connect to the Oracle database. What would you check?

• Check if the database is up (i.e., ps -ef | grep pmon).
• Check the listener status by running lsnrctl status.
• Check the TNS configuration (tnsnames.ora, sqlnet.ora) to see if it is configured correctly.
• Check for firewall or network issues.
• Lastly, check if the user account is locked or expired.

Q48. Scenario: You need to migrate a 500GB Oracle database with minimal downtime. How would you approach this?

• Your option would be to use Oracle Data Pump with a parallel option so that it would be as fast as possible.
• For very large data sets, use transportable tablespaces.
• For minimal downtime, use Oracle GoldenGate for real-time replication.
• Before migrating, do a migration test, followed by validation against checksums.

Q49. Scenario: How would you find out which SQL statements have the highest CPU usage? 

Check CPU-heavy SQL using V$SQL and V$SQLAREA. Run AWR or ADDM reports for more SQL performance statistics. Use SQL trace (TKPROF) or DBMS_MONITOR to analyse execution. Tune or rewrite the offending queries.

Q50. Scenario: A scheduled job failed last night. What steps would you take to identify the root cause of the issue? 

• Look at job logs in DBA_SCHEDULER_JOB_RUN_DETAILS. 
• Check for errors in DBA_SCHEDULER_JOB_LOG. 
• Review the database alert logs and trace files. 
• Re-run the job manually to see if you can replicate the issue. 
• Fix anything you see that could have caused the job to fail, e.g., permissions, missing objects, or data issues.

Q51. Scenario: You have a large table, and it is growing rapidly. What do you do? 

Review the table growth pattern using the AWR report or historical statistics. Consider partitioning the table for better manageability or performance on queries. Purge old data or move any archival data into another table/tablespace. Alternatively, compress the table using Advanced Compression (if licensed). 

Q52. Scenario: A developer asks for a report of all failed login attempts. What steps do you take to provide this?

Enable auditing using the AUDIT SESSION WHENEVER NOT SUCCESSFUL functionality. Query DBA_AUDIT_SESSION for failed login attempts. If using Unified Auditing, query the UNIFIED_AUDIT_TRAIL. Format and export the data in SQL.

Q53. Scenario: You have identified a session that is locking a table and blocking others; what are your steps to resolve?

• Identify blocking sessions by checking V$SESSION and V$LOCK.
• You can run SELECT * FROM dba_blockers and dba_waiters.
• You can use ALTER SYSTEM KILL SESSION to kill the session if required.
• Review application logic to avoid table locking in the future.

Q54. Scenario: You have a materialised view that is not refreshing; what would be your steps to troubleshoot the issue?

Check the statuses in DBA_MVIEWS to see if it is in a valid status or which refresh method is being used. If it is associated with a scheduled job, then check DBA_JOBS or DBA_SCHEDULED_JOBS. You might have to check the dependencies (like dropped objects in the event a view is marked invalid) or manually refresh it and check alert logs or USER_ERRORS for warnings or error messages.

Q55. Scenario: You have to clone a production database to a NON-PROD (test) instance; what would you do?

You can use the RMAN DUPLICATE command to clone the production database or use Data Pump to clone (at the schema level) the database into the NON-PROD instance, sanitising or masking any sensitive data once completed. You would then change parameters (like DB_NAME, service names, etc.) for the NON-PROD environment.

Technical Interview Questions

Q56. How do you find the second-highest salary in a table?

SELECT MAX(salary) AS Second_Highest_Salary
FROM employees
WHERE salary < (SELECT MAX(salary) FROM employees);

Q57. How do you find duplicate records in a table?

SELECT employee_id, COUNT(*)
FROM employees
GROUP BY employee_id
HAVING COUNT(*) > 1;

Q58. How to retrieve the top N records in Oracle?

SELECT * FROM (
  SELECT * FROM employees ORDER BY salary DESC
)
WHERE ROWNUM <= 5;

Q59. How to update a column using a correlated subquery?

UPDATE employees e
SET salary = (
  SELECT salary * 1.1
  FROM departments d
  WHERE e.department_id = d.department_id
)
WHERE EXISTS (
  SELECT 1 FROM departments d WHERE e.department_id = d.department_id
);

Q60. How do you display employees with the highest salary in each department?

SELECT * FROM employees e
WHERE salary = (
  SELECT MAX(salary)
  FROM employees
  WHERE department_id = e.department_id
);

Q61. How do you delete duplicate rows but keep one?

DELETE FROM employees
WHERE ROWID NOT IN (
  SELECT MIN(ROWID)
  FROM employees
  GROUP BY employee_id
);

Q62. How to use the CASE statement in a SELECT query?

SELECT employee_name,
  CASE 
    WHEN salary < 3000 THEN 'Low'
    WHEN salary BETWEEN 3000 AND 7000 THEN 'Medium'
    ELSE 'High'
  END AS salary_grade
FROM employees;

Q63. How to find all employees who joined in the last 6 months?

SELECT * 
FROM employees
WHERE hire_date >= ADD_MONTHS(SYSDATE, -6);

Q64. How to get the count of employees in each department with total salary?

SELECT department_id, COUNT(*) AS total_employees, SUM(salary) AS total_salary
FROM employees
GROUP BY department_id;

Q65. How to use analytical functions in Oracle to rank employees by salary?

SELECT employee_name, department_id, salary,
  RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) AS salary_rank
FROM employees;

Behavioural Oracle Interview Questions

Q66. Can you describe a time you were able to solve a critical database problem when you were under a lot of pressure? What was your approach?

We were in the middle of peak business hours when suddenly the production database cropped up and started slowing down. I quickly logged into the database, checked the appropriate AWR and ADDM reports, and discovered a runaway query. I terminated the runaway session and analysed the SQL code, optimised the relevant indexes, and worked with the development team to find a permanent fix. The key was staying calm and relaxing and using my structured approach, so I was able to resolve the issue quickly.

Q67. Please tell us about a difficult Oracle migration you managed. What parts of the planning helped with the success? 

We were tasked with migrating a 1TB Oracle database from an on-premise server to the Oracle Cloud in real-time with very little downtime. I led the planning, utilised Oracle Data Pump with a pre-load for the downtime period, used Oracle Golden Gate for the live replication, performed multiple test runs, and we had a bona fide rollback plan. When it came time for the final cutover, we completed it flawlessly ahead of schedule. 

Q68. How do you handle disagreements with developers about database performance issues? 

I keep it collaborative, not accusatory. I have encountered many performance issues with developers involving the database. I present my findings with appropriate evidence (execution plans, statistics, etc.), if their SQL code is the cause. I openly discuss potential optimisations and recommend what I believe is the best solution to resolve the issue. At the end of the day, we are trying to work together to support the business and not to figure out who’s right or wrong. 

Q69. Can you tell us about an occasion you implemented a new process or the process that enhanced your team's productivity with Oracle?

I developed AWR and SQL Monitor dashboards for proactive performance monitoring. It improved our response time, allowing us to catch problems and address them before users found any issues. We were able to reduce incident tickets by about 40%, and we had more time to spend on tuning and less on firefighting.

Q70. Discuss a time when you needed to quickly learn a new Oracle feature so you could meet a project deadline.

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