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Preparing for an Oracle interview can be an intimidating yet enjoyable undertaking due to the extensive array of Oracle database technologies. Familiarity with fundamental and advanced principles is crucial for becoming an Oracle database administrator, developer, or architect. Interview questions posed by Oracle can be intricate, ranging from foundational concepts for novices to sophisticated scenario-based inquiries that evaluate practical understanding. In this article, you will enhance your preparation and approach your upcoming Oracle interview with greater assurance.

Table of Contents:

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

What is Oracle?

Oracle is a prominent technology firm, and one of its flagship offerings is the Oracle Database, an enterprise-grade relational database management system (RDBMS). The Oracle Database is designed to efficiently store, manage, and retrieve substantial amounts of data in a multi-user environment. Oracle employs Structured Query Language (SQL) and PL/SQL for data manipulation and is utilized across various sectors, such as finance, healthcare, retail, and public services. Beyond its database offerings, Oracle boasts a vast array of cloud solutions, enterprise applications (like Oracle E-Business Suite), and development tools, establishing itself as a key player in enterprise IT.

Recruitment Process of Oracle

1. Application: Submit your CV through Oracle’s career platform or via employee referrals.
2. Online Assessment: Comprises coding questions (Java/SQL), aptitude tests, and problem-solving scenarios.
3. Technical Rounds: Emphasizes SQL/PLSQL coding, principles of database design, and inquiries related to Oracle Cloud Infrastructure (OCI).
4. Behavioral Round: Utilizes STAR-method questions to evaluate teamwork, adaptability, and problem-solving skills.
5. HR Discussion: Includes salary discussions, role expectations, and the onboarding process.

Oracle Interview Questions

Oracle interview inquiries can be divided into fundamental questions for novices, intermediate questions, advanced questions for seasoned candidates, scenario-based questions, technical questions, and behavioral 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 effectively store, manage, and retrieve sizable volumes of structured data and supports SQL for querying.

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

A Relational Database Management System is software specifically designed to manage and manipulate data organized in rows and columns across multiple tables. RDBMSs inherently maintain data integrity and execute database functions such as inserting, updating, deleting, and querying data, primarily through the query language Structured Query Language (SQL).

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

Common types of Oracle database objects include tables, views, indexes, sequences, synonyms, procedures, functions, packages, and triggers.

Q4. What is a table in Oracle?

A table is an Oracle object used for storing data in rows and columns, where each row signifies a record and each column signifies a data field.

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

Oracle has designated the VARCHAR datatype for future applications. VARCHAR currently functions like VARCHAR2 in existing releases of the Oracle database; however, in upcoming releases, VARCHAR may behave differently from VARCHAR2.

Q6. What is a primary key?

A primary key is a column or set of columns that uniquely distinguishes each row in a table. A primary key cannot contain any null values, but can include unique values.

Q7. What is a foreign key in Oracle?

A foreign key refers to a column that establishes a relationship between two tables by referencing the primary key in another table. The foreign key ensures referential integrity.

Q8. What is a view? How is it different from a table?

A view acts as a ‘virtual’ table derived from the result of a SQL query. Unlike a table, a view does not physically store data; it presents the information stored in one or more tables.

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

There are five physical components in Oracle Database:

• Parameter files
• Data files
• Control files
• Redo log files
• Password files

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

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Constraints are regulations that dictate specific actions imposed on the data within tables. Various types consist of:  

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

Q11. What distinguishes DELETE, TRUNCATE, and DROP?

• DELETE: Erases specific rows according to a defined condition and can be reverted.
• TRUNCATE: Rapidly eliminates all rows compared to DELETE; cannot be reverted.
• DROP: Permanently deletes the table structure along with its data.

Q13. What is an index in Oracle, and what is its purpose?
An index is a database entity that enhances the speed of data retrieval. It serves as a reference to data within a table, minimizing the necessity to scan the entire table.

Q14. What varieties of joins exist in Oracle SQL?

There exist several types of joins in Oracle SQL.

1. INNER JOIN – Returns rows with corresponding values in both tables.
2. LEFT JOIN – Returns all rows from the left table along with matching rows from the right.
3. RIGHT JOIN – Returns all rows from the right table plus matching rows from the left.
4. FULL OUTER JOIN – Returns all rows when there is a match in one of the tables.
5. CROSS JOIN – Returns the Cartesian product of both tables.

Intermediate Interview Questions

Q15. What is the distinction between a view and a materialised view in Oracle? 

A view is a virtual table derived from a SQL query. It does not hold any data. In contrast, a materialised view physically retains the result of a query, enabling periodic data refreshes.

Q16. Describe an Oracle tablespace.

A tablespace is a logical storage component within an Oracle database. An Oracle tablespace comprises one or more datafiles and offers storage allocations for schema objects, including tables and indexes.

Q17. What are the various types of indexes in Oracle?

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

Q18. What differentiates TRUNCATE from DELETE in Oracle?

DELETE is a DML operation, can be reverted, and activates triggers, whereas TRUNCATE is a DDL operation, cannot be reverted, and does not trigger activation.

Q19. Outline the components of Oracle architecture.

Oracle architecture components include the Oracle Instance comprising the System Global Area (SGA) alongside background processes. The database consists of datafiles, redo log files, control files, and user processes.

Q20. What are sequences in Oracle? When are they utilized?

In Oracle, a sequence is a database object designed to generate unique numbers automatically, typically for primary key values. It helps prevent locking issues by producing IDs independently of table data. Sequences are frequently employed in multi-user environments to guarantee swift and secure ID generation.

Q21. What is Oracle Data Pump, and how does it contrast with EXP/IMP?

Oracle Data Pump (utilizing expdp and impdp) is an expedited utility for exporting and importing database objects. It is quicker than the older EXP/IMP, supports parallel execution, improved filtering, and direct path loading, establishing it as the favored and more effective approach for data transfer.

Q22. How does Oracle handle locking and concurrency? 

Oracle employs Multi-Version Concurrency Control (MVCC) to ensure users can access consistent data without delays. It manages locking at the row-level, permitting multiple users to read and write simultaneously while avoiding conflicts and upholding data integrity.

Q23. What is the difference between %TYPE and %ROWTYPE in PL/SQL? 

%TYPE is utilized to declare a variable with the same data type as a specified column, while %ROWTYPE allows you to declare a record matching the structure of a row in a table or cursor, inclusive of all its columns and their types.

Q24. Compare the RANK() and DENSE_RANK() functions. 

Both are analytic functions in SQL utilized to rank rows based on a specific column. RANK() assigns identical ranks to tied values but omits the subsequent ranks, creating gaps. DENSE_RANK() also assigns the same rank to ties but proceeds with the subsequent number, ensuring no gaps occur in the ranking.

Advanced Interview Questions for Experienced

Q25. What is Dynamic SQL in Oracle?

Dynamic SQL refers to the capability to construct and execute SQL statements at runtime. It is applied when the exact SQL statement isn’t predetermined until execution time. Dynamic SQL is executed using the EXECUTE IMMEDIATE command or via the DBMS_SQL package.

Q26. How does BULK COLLECT enhance performance?

BULK COLLECT enables the program to retrieve multiple rows simultaneously utilizing a single context switch from SQL to PL/SQL engine, which proves invaluable for fetching substantial data amounts.

Q27. What is FORALL in PL/SQL?

FORALL is a construct designed to optimize context switching during DML operations enacted within a loop. FORALL works with collections and conducts DML operations in bulk to enhance performance while employing DML in a loop.

Q28. Define the term Autonomous Transactions.

An autonomous transaction is a self-sufficient transaction initiated by another transaction. Autonomous transactions can commit or revert independently and do not affect the main (parent) transaction. They are declared using the PRAGMA AUTONOMOUS_TRANSACTION command and are beneficial when logging or auditing operations require independent commitment.

Q29. How do you manage exceptions in PL/SQL?

In PL/SQL, exceptions can be managed using the EXCEPTION block. Oracle possesses predefined exceptions like NO_DATA_FOUND, and user-defined exceptions may be declared and raised, accomplished by utilizing the RAISE command.

Q30. What is the purpose of the DBMS_STATS package? 

The DBMS_STATS package is employed to gather and oversee statistics crucial for the cost-based optimizer, enabling informed choices regarding the most efficient method to execute a query. The more precise the data statistics, the better the execution plans generated for a particular SQL query.

Q31. What are Global Temporary Tables (GTT)?

Global Temporary Tables (GTT) retain session-private data that vanishes when the session concludes (for instance) or the transaction ends. They are commonly used for temporarily storing intermediate results within the GTT. GTTs can be defined with ON COMMIT DELETE ROWS (transaction-level) or ON COMMIT PRESERVE ROWS (session-level).

Q32. How do you prevent deadlocks in Oracle?

Here are some best practices to avert …
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deadlocks in Oracle databases: 

• Access your tables in a uniform sequence throughout all transactions.
• Keep your transactions brief whenever possible and commit as soon as you can.
• Maintain appropriate locking practices on your side.
• Avoid prolonged transactions and refrain from merely delaying commits.

Q33. What is a REF CURSOR, and when would you employ it?

A REF CURSOR is a reference to a query result set that enables dynamic and adaptable data retrieval. It is utilized when the query structure is variable or when transferring result sets between PL/SQL blocks and external applications like Java or Python.

Q34. How do Analytical Functions differ from Aggregate Functions?

For instance, analytical functions (RANK(), LEAD(), LAG()) calculate values over a specified window of rows without collapsing the result set. Aggregate functions (SUM(), AVG(), etc.) yield a single value for each group of records.

Q35. What is Oracle Partitioning, and what advantages does it offer?

Partitioning refers to the method of dividing a table into smaller, more manageable segments known as partitions. This technique can enhance performance for queries, facilitate manageability, and ease maintenance when handling extensive data.

Q36. What methods do you use to optimize a slow-performing SQL query in Oracle?

The optimization process involves examining execution plans, reviewing statistics using DBMS_STATS, and implementing suitable indexes. It also includes avoiding full table scans, rewriting or rearranging queries to increase efficiency by modifying the types of joins.

Q37. What distinguishes hot backup from cold backup in Oracle?

A hot backup occurs while the database operates in ARCHIVELOG mode, allowing continuous access. A cold backup is performed while the database is shut down, ensuring the database remains in a consistent state.

Q38. Explain Oracle Data Guard and its various types.

Oracle Data Guard offers data protection and disaster recovery solutions through the utilization of both primary and standby databases. The standby databases are categorized into Physical standby, Logical standby, and Snapshot standby.

Q39. What are AWR, ASH, and ADDM reports?

• AWR (Automatic Workload Repository) collects data on database performance.
• ASH (Active Session History) monitors database performance but only for active sessions.
• ADDM (Automatic Database Diagnostic Monitor) utilizes information from AWR to identify performance problems.

Q40. How do you address locking and blocking complications?

To identify blocking sessions, examine v$session, v$lock, or utilize various Enterprise Manager tools. To resolve blocking issues, you may need to terminate sessions, modify your transaction structure, or establish a locking strategy.

Q41. How do you monitor and adjust memory in Oracle?

Auto memory management is beneficial, but you can also inspect SGA and PGA to comprehend allocation and memory usage by reviewing v$SGA_DYNAMIC_COMPONENTS and v$PGA_TARGET_ADVICE. Tuning MEMORY_TARGET and SGA_TARGET may also be necessary.

Q42. What is your approach for database migration?

Migration involves planning and utilizing tools like Data Pump (expdp/impdp), RMAN, or GoldenGate to minimize downtime. Implementing thorough testing and rollback protocols should be integral to the process prior to deployment into production.

Q43. How do you establish security on an Oracle database?

Apply the principle of least privilege through roles, user profiles, auditing (via the AUDIT command or the Unified Audit Trail), and encryption (TDE). Additionally, ensure security on the network level (Oracle Net Services).

Q44. What are bind variables, and why are they significant?

Bind variables assist in preventing SQL injection and boost performance by reusing SQL statements. They help avoid hard parsing by enabling the reuse of optimized cached execution plans.

Q45. How do the NOLOGGING and LOGGING options differ in Oracle?

NOLOGGING minimizes the volume of redo logs generated, which benefits bulk insert operations. However, NOLOGGING may result in data loss during recovery. LOGGING records actions in redo logs, ensuring recovery is always possible.

Q46. How do you utilize Oracle’s Resource Manager?

Oracle Resource Manager allows for prioritizing CPU and I/O resources among sessions. Resource plans are employed to manage resources so that runaway queries cannot monopolize system resources.

Scenario-Based Interview Questions

Q47. Scenario: A crucial query is executing significantly slowly in production. How would you troubleshoot?

• The first step is to capture the execution plan using EXPLAIN PLAN or DBMS_XPLAN.DISPLAY_CURSOR.
• Next, I will verify the statistics for the tables used through DBMS_STATS.
• After that, I will review AWR/ASH reports to assess system performance.
• Once I have completed those checks, I may analyze the indexes and consider rewriting the query or employing hints.
• If performance issues persist, I will investigate for contention or locks on resources.

Q48. Scenario: A user reports they cannot connect to the Oracle database. What would you verify?

• Check if the database is operational (i.e., ps -ef | grep pmon).
• Validate the listener status by executing lsnrctl status.
• Review the TNS configuration (tnsnames.ora, sqlnet.ora) for correctness.
• Investigate potential firewall or network complications.
• Finally, check whether the user account is locked or has expired.

Q49. Scenario: You need to transfer a 500GB Oracle database with minimal downtime. How would you proceed?

• Utilize Oracle Data Pump with a parallel option to maximize speed.
• For very large datasets, leverage transportable tablespaces.
• For minimal downtime, implement Oracle GoldenGate for real-time replication.
• Prior to migration, conduct a migration test, followed by validation against checksums.

Q50. Scenario: How would you identify which SQL statements consume the most CPU?

Examine CPU-intensive SQL via V$SQL and V$SQLAREA. Generate AWR or ADDM reports for additional SQL performance insights. Use SQL trace (TKPROF) or DBMS_MONITOR for execution analysis. Optimize or revise the problematic queries.

Q51. Scenario: A scheduled job failed last night. What steps would you take to determine the root cause of the issue?

• Review the job logs in DBA_SCHEDULER_JOB_RUN_DETAILS.
• Check…
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  for discrepancies in DBA_SCHEDULER_JOB_LOG. 
• Examine the database alert logs and trace files. 
• Execute the job manually to determine if you can replicate the problem. 
• Correct any issues you observe that might have led to the job’s failure, such as permissions, absent objects, or data discrepancies.

Q52. Scenario: You have a substantial table that is expanding swiftly. What are your next steps? 

Analyze the table’s growth trend utilizing the AWR report or historical statistics. Consider partitioning the table to enhance manageability or performance for queries. Delete outdated data or transfer any archival information to another table/tablespace. Alternatively, compress the table utilizing Advanced Compression (if licensed). 

Q53. Scenario: A developer requests a report of all unsuccessful login attempts. What actions will you take to provide this? 

Activate auditing through the AUDIT SESSION WHENEVER NOT SUCCESSFUL feature. Query DBA_AUDIT_SESSION for failed login entries. If employing Unified Auditing, query the UNIFIED_AUDIT_TRAIL. Format and export the data using SQL.

Q54. Scenario: You have pinpointed a session that is locking a table and obstructing others; what measures will you take to resolve this? 

• Identify blocking sessions by examining V$SESSION and V$LOCK.
• You can execute SELECT * FROM dba_blockers and dba_waiters.
• Employ ALTER SYSTEM KILL SESSION to terminate the session if needed.
• Review application logic to prevent future table locking.

Q55. Scenario: You have a materialized view that is not refreshing; what steps would you take to diagnose the problem?

Inspect the statuses in DBA_MVIEWS to determine if it is in a valid state or which refresh method is being utilized. If it is linked to a scheduled job, check DBA_JOBS or DBA_SCHEDULED_JOBS. You may need to review dependencies (such as dropped objects if a view is marked invalid) or manually refresh it and inspect alert logs or USER_ERRORS for any warnings or error messages.

Q56. Scenario: You are tasked to clone a production database to a NON-PROD (test) instance; what actions would you pursue?

You can utilize the RMAN DUPLICATE command to clone the production database or employ Data Pump to clone (at the schema level) the database into the NON-PROD instance, ensuring any sensitive data is sanitized or masked upon completion. Subsequently, you would adjust parameters (such as DB_NAME, service names, etc.) for the NON-PROD environment.

Technical Interview Questions

Q57. How do you retrieve the second-highest salary in a table?

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

Q58. How do you identify duplicate records in a table?

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

Q59. How to fetch the top N records in Oracle?

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

Q60. How to modify 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
);

Q61. 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
);

Q62. How do you eliminate duplicate rows while retaining one?

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

Q63. How to implement 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;

Q64. How to find all employees who joined within the last 6 months?

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

Q65. How to calculate the count of employees in each department along with total salary?

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

Q66. How to utilize 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

Q67. Can you recount a moment you resolved a critical database issue while under significant pressure? What was your method?

During peak business hours, the production database encountered performance issues and began to lag. I promptly logged into the database, assessed the relevant AWR and ADDM reports, and uncovered a runaway query. I halted the runaway session, analyzed the SQL code, optimized the necessary indexes, and collaborated with the development team for a long-lasting solution. The crucial aspect was maintaining composure and employing my structured methodology, which enabled me to address the issue swiftly.

Q68. Please share an experience regarding a challenging Oracle migration you oversaw. Which aspects of the planning contributed to its success? 

We were instructed to migrate a 1TB Oracle database from an on-premise server to the Oracle Cloud in real-time with minimal downtime. I spearheaded the planning and utilized Oracle Data Pump with a pre-load for the downtime period, incorporating Oracle Golden Gate for live replication, conducting multiple test scenarios, and ensuring we had a comprehensive rollback plan. When it was time for the final transition, we executed it flawlessly and ahead of schedule. 

Q69. How do you resolve disagreements with developers regarding database performance concerns? 

I maintain a collaborative approach rather than a confrontational one. I have encountered numerous performance challenges with developers related to the database. I present my discoveries backed by substantial evidence (execution plans, statistics, etc.) if their SQL code is at fault. I engage in open discussions about possible optimizations and suggest what I view as the most effective solution to remedy the issue. In the end, we aim to work together in support of the business rather than determining who is right or wrong. 

Q70. Can you describe a time you implemented a new procedure that improved your team’s efficiency with Oracle?

I developed AWR and SQL Monitor dashboards for proactive performance oversight. This initiative enhanced our response times, enabling us to detect and address issues before users experienced any disruptions. We successfully decreased incident tickets by approximately 40%, allowing us to allocate more time to tuning rather than firefighting.

Q71. Recall an instance when you had to rapidly acquire knowledge of a new Oracle feature to meet a project deadline.

When…
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We were required to deploy Oracle Data Masking for regulatory compliance, and I had limited familiarity with it. I perused documentation and engaged in practical exercises and scenarios throughout the weekend. By Monday, I had a functional prototype, which we subsequently enhanced and launched. It was an excellent instance of acquiring knowledge and managing stress.

Oracle Developer Anticipated Salary

Experience Level	Salary Range (INR per year)	Salary Range (USD per year)
Entry-Level	₹6,00,000 – ₹10,00,000	$7,229 – $12,048
Mid-Level	₹12,00,000 – ₹18,00,000	$14,458 – $21,686
Senior Level	₹22,00,000 – ₹37,00,000	$26,530 – $44,578

The salary figures were derived from data collected on Glassdoor.

Closing Thoughts

To adequately prepare for an Oracle interview and excel, it’s essential to grasp fundamental concepts (SQL, PL/SQL, architecture) and implement them through hands-on skills such as performance optimization and troubleshooting. This document contains Oracle interview inquiries that span all levels for different positions including DBA, developer, and architect. A key aspect of your preparation will be to perform ample practical exercises and comprehend overarching principles, in addition to problem-solving skills, to demonstrate your technical proficiency. If you’ve engaged in sufficient practice, you will be well-equipped to show the interviewer that you possess both experience, understanding, and practical capabilities necessary for the position.

Leading Oracle Interview Questions – FAQs

The article Top Oracle Interview Questions first appeared on Intellipaat Blog.

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