Top 30+ Oracle Interview Questions and Answers

About Oracle

Headquartered in Austin, Texas, Oracle is an American multinational computer technology firm that offers cloud engineered systems, enterprise software products, database software and technology, and database management systems. The company develops tools for database development, enterprise resource planning (ERP) software, human capital management (HCM) software, customer relationship management (CRM) software, enterprise performance management (EPM) software, and supply chain management (SCM) software.

Oracle Interview Process

Oracle’s hiring team builds an inclusive workplace and hires highly skilled people from different relevant backgrounds. Oracle recruiters seek polished problem-solvers who can tackle modern-day problems via sound analytical skills.

Interview Rounds

• Online Coding Round: The first round is an online test comprising multiple choice questions ranging from quantitative analysis and logical reasoning to important concepts like data structures and algorithms, OOPs, networking, and database management systems. 
• The Initial Phone Screen: During this second round, a recruiter from human resources assesses a candidate’s skills and experience. 
• Technical Interview Round: The coding skills are evaluated. A candidate will have to answer two Oracle interview questions based on data structures and algorithms. Technical questions, puzzles, and past projects are explored in this round.
• HR Round: The interviewer questions the candidate’s work experience and ethics to decide whether the applicant is a cultural fit for the organisation.

Basic Oracle Interview Questions

1. What are schema objects?

Schema objects are tables, indexes, databases, views, sequences, synonyms, triggers, functions, procedures, and packages.

2. What are the components of physical database structure in the Oracle database?

The components of the physical database structure are: 

• Greater than equal to two redo log files.
• Greater than equal to one control file.
• Greater than equal to one data file.

3. What are the components of logical database structure in Oracle database?

The two main components of logical database structure in the Oracle database are: 

• Tablespaces
• Database's schema objects

A tablespace is the logical storage unit of an Oracle database. It is a set of related logical structures. The default tablespaces are: 

• SYSTEM and SYSAUX tablespaces 
• USERS tablespace
• UNDOTBS1 tablespace
• TEMP tablespace 

4. Differentiate between Varchar and varchar2.

Varchar and Varchar2 are data types in Oracle to store character strings of varying lengths. While Varchar can store characters up to 2000 bytes, Varchar2 can store up to 4000 bytes. Varchar will hold space for all characters defined during declaration. Varchar2 will free up the space for characters that were unused.

5. What is an Oracle table?

A table is the basic unit of data storage in the Oracle database. Data is stored in rows and columns. 

“CREATE TABLE” statement is used to create a new table. 

6. What is a nested table?

Nested table is a data type in Oracle used to hold columns for storing multi-valued attributes. A nested table can hold an entire sub table. 

7. How are comments represented in Oracle?

We can represent comments in Oracle in the following two ways:

Two dashes (–) before the line starts – Single statement

For block of statement, we can use /*—— */ to represent it as comments 

8. What is the relationship between database, tablespace and data file?

An Oracle database can contain one or more tablespaces or logical storage units. These tablespaces collectively store all the data in a database. Each tablespace consists of one or more files called data files. The data files are physical structures conforming to the operating system in which Oracle is running.

9. What are database objects in Oracle?

Various Oracle database objects are:

Tables – set of elements arranged in vertical and horizontal manner

Tablespaces – logical storage unit

Views – Virtual table derived from one or more tables.

Indexes – performance tuning method for record processing.

Synonyms – name for tables

10. Explain the ANALYZE command in Oracle.

The “ANALYZE” command allows the user to perform various functions on index, table or cluster. It helps: 

To identify migrated and chained rows of the table or cluster.

To validate structure of an object

To collect statistics about objects used by user, which are then stored onto the data dictionary

To delete statistics used by an object from the data dictionary

11. What types of Joins are used in SUBQUERIES?

A join is used to compare and combine specific rows of data from two or more tables in a database. The various joins are:

Self Join – to join table with itself

Outer Join – to join matching data and some dissimilar data from more than one table

Equi-join – with a join condition that returns only rows with equivalent values

12. What is DML?

We use Data Manipulation Language or DML to access and handle data in the existing objects. The DML statements are select, insert, update, and delete.

RAW datatype in Oracle

The RAW datatype stores variable-length binary data or byte string values. The maximum size for a raw in a table is 32767 bytes.

13. What are Aggregate functions in Oracle?

In an aggregate function, multiple rows or records are combined, and operations performed on a set of values to get a single value as output. Common aggregate functions include:

Sum

Count

Average

14. What are Temporal data types?

Date Datatype

Time Stamp Datatype

Interval Datatype

15. What is a View?

View is a logical table based on one or more tables or views. A view does not store data physically. Tables upon which views are based are called Base tables. 

16. How are pictures stored onto a database?

Long Raw Data type can be used to store pictures onto a database. Binary data of length 2GB can be stored using this datatype. 

17. Where do you use DECODE and CASE statements?

These statements function like the if-then-else statement and are used in Oracle for data value transformation. 

18. What is MERGE in Oracle, and how can you merge two tables?

Merge statement allows merging data from two tables subsequently. It selects data from the source table and inserts/updates the data in the destination table as per the condition specified in the query. Merge command is useful in Data warehousing applications. 

19. What is NULL value in Oracle?

NULL value indicates missing or unknown data. 

20. When is a SYSTEM tablespace created?

A SYSTEM tablespace is automatically generated when any database is created in the Oracle database system. It contains the data dictionary tables for the entire database and always remains online.

21. What does each number represent in the Oracle version 9.3.0.5.0?

Oracle version number represents the following: 

• 9 - Major database release number
• 3 - Database maintenance release number
• 0 - Application server release number
• 5 - Component Specific release number
• 0 - Platform Specific release number

22. What is a bulk copy in Oracle?

Bulk copy or BCP is for importing and exporting data from tables and views. It doesn't copy the structure of the same data. It has a quick mechanism for copying data and allows the users to easily take the data backup.

Intermediate Oracle Interview Questions

23. What is Integrity Constraint?

Integrity constraint is a declaration to define a business rule for a table column. It ensures data accuracy and consistency. Common types are:

Domain Integrity

Referential Integrity

24. What is SQL?

SQL or Structured Query Language is used to communicate with the server for accessing, manipulating, and controlling data. 

25. What are the different types of SQL statements?

The five types of SQL statements are:

Data Definition Language (DDL): CREATE, DROP, RENAME, ALTER, TRUNCATE

Data Manipulation Language (DML): INSERT, DELETE, UPDATE, MERGE

Data Control Language (DCL): GRANT, REVOKE

Data Retrieval: SELECT

Transaction Control Statements: COMMIT, SAVEPOINT, ROLLBACK

26. What is PL/SQL?

PL/SQL is an extension of SQL, which is used in Oracle. PL/SQL combines SQL’s data manipulation power with the processing power of procedural language and creates extra-powerful SQL queries. It uses SQL to instruct the compiler what to do and a procedural way to instruct how to do it. 

27. What is a Literal?

A Literal is a string consisting of a character, a number, or a date that is included in the Select list but which is not a column name or alias.  

28. Difference between SQL and iSQL*Plus?

SQL is a language, but iSQL*Plus is an environment. iSQL*Plus is a command line tool that allows typing SQL commands to be executed directly against the Oracle database. While SQL uses Functions to perform certain formatting, iSQL*Plus uses commands to format data. 

29. What are SQL functions?   

SQL functions can take arguments but always return a certain value. The 2 types of SQL functions are:

Single-row functions like character, number, date, conversion, and general. 

Multiple-row functions like avg, count, sum, max, min, stddev, variance.

Types of SQL General functions are:

NVL

NVL2

NULLIF

COALESCE

Conditional Expressions

30. What is a Sub Query?

A SELECT statement embedded within a clause of another SELECT statement is called a subquery. It can be placed in WHERE, HAVING, and FROM clause. 

31. What is VArray?

VArray (variable sized array) is an Oracle datatype used to hold columns containing multi-valued attributes. It can hold a bounded array of values. 

Advanced Oracle Interview Questions

32. What is the fastest query method to fetch data from a table?

Using the Row ID is the fastest query method to fetch data from a table. 

33. What is the difference between hot backup and cold backup?

Hot backup is also called online backup, as it is done when the database is active. 

Cold backup is also called offline backup, as it is done when the database has been shutdown. 

34. What are the uses of a database trigger?

Triggers are programs that get automatically executed in response to some events. For example, a trigger can be invoked when a row is inserted into a table. It helps maintain data integrity. 

35. What is the difference between TRANSLATE and REPLACE?

TRANSLATE is used to substitute a character by a character, while REPLACE is used to substitute a character with a word. 

36. What is Cross Join?

Cross join is the Cartesian product of records from the tables that are there in the join. 

Other Oracle Interview Questions for Experienced

1. What are the various modules in Oracle forms?
2. What does a snapshot in the Oracle database mean?
3. How many memory layers does the Oracle shared pool have?
4. What do the terms save point and hash cluster mean in the Oracle database?
5. What are the different types of Oracle database objects?
6. Enumerate the differences between pre-select and pre-query.
7. What is a synonym? Can you create a synonym without a table?
8. State the different types of synonyms and their use. 
9. What is the significance of the control file in Oracle?
10. What does BLOB data type mean in Oracle?
11. How is a post-database commit different from a post-form commit?
12. What is a logical backup?
13. What is redo log file mirroring in Oracle?
14. What are recursive hints in Oracle?
15. State the limitations of the CHECK constraint.
16. How would you convert a date to char in Oracle? Explain with an example.
17. What do you understand about formal and actual parameters?
18. What extensions do Oracle reports use?
19. How would you convert a string to a date in the Oracle database?
20. How would you find the current time and date in Oracle?
21. What is the use of the following options in the IMP command: 
1. ROWS
2. GRANT
3. INDEXES 
4. IGNORE 
5. SHOW 
6. FILE param 

FAQs

1. How many rounds does an Oracle interview have for a software engineer?

Oracle interview usually has three to four rounds:

• Online Coding Round
• Technical Round (2 Rounds)
• HR Round

2. How to answer the question: why do you want to join Oracle?

A candidate can have several reasons to join Oracle. Include the most prominent ones in your answer to this Oracle interview questions:

• It offers high-quality products and presents a vast range of opportunities for employees to learn.  
• The work culture is collaborative. 
• Candidates find themselves standing on the frontline of digital transformation that helps them show their truly inquisitive minds.

3. Are Oracle interviews hard?

The level of interview preparation makes the process appear easy or hard. Usually, the Oracle interview questions are of easy to medium level. However, the incorporation of several interview rounds can make the interview challenging for some candidates. A solid preparation strategy and consistent practice make it easy to nail the interview. 

4. What questions should I ask the interviewer at Oracle?

To appear confident and convey your interest in the job opportunity, it is always a good option to ask a few questions such as:

• The company’s culture 
• What technology is it opting for making its latest products?
• The future innovations
• The team you will be working with 

5. What are the most famous products of Oracle?

The famous products of Oracle are as follows:

• Oracle Database
• Siebel
• PeopleSoft Enterprise
• Oracle E-Business Suite
• Oracle JDeveloper, a freeware IDE

6. What skills are required for an Oracle developer position?

Oracle seeks software developers with a sound knowledge of Java, SQL databases, cloud technologies, and software engineering models, such as Agile Method, Waterfall Method, and more. 

7. How long is the Oracle hiring process? 

Once a candidate clears all the technical rounds, they must submit all educational certificates and other documents like salary slips and past employment certificates. After the interview, Oracle takes between 45 days to 60 days for background verification. From the first interview round to the day of joining, the entire hiring process takes up to 120 days on average. 

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