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Table of contents
1.
About Oracle
2.
Top Oracle Interview Questions
2.1.
1. Using which language is the Oracle database developed?
2.2.
2. What is tablespace with respect to the Oracle database?
2.3.
3. Define the Oracle table.
2.4.
4. Give uses of a control file.
2.5.
5. Differentiate between VARCHAR & VARCHAR2?
2.6.
6. Differentiate between a hot and cold backup in Oracle and tell about their benefits.
2.7.
7. Define various Oracle database objects.
2.8.
8. Define COALESCE function?
2.9.
9. Tell about the various constraints in Oracle.
2.10.
10. Describe the Redo Log file mirroring?
2.11.
11. Differentiate between SQL and iSQL*Plus?
2.12.
12. In SQL queries, what is the purpose of the double ampersand (&&)? Could you give an example?
2.13.
13. Describe the temporal data types in Oracle.
2.14.
14. Write code to display row numbers with records.
2.15.
15. Describe the save point in the Oracle database.
2.16.
16. Differentiate between PL SQL and SQL?
2.17.
17. Describe the order of precedence which is used in executing SQL statements?
2.18.
18. Describe the uses of ANALYZE command.
2.19.
19. Explain about types of snapshots.
2.20.
20. What is the definition of a transaction? Describe the most common errors that can occur during the execution of any transaction.
2.21.
21. In Oracle, what is a bulk copy or BCP?
2.22.
22. In SQL, what is locking? What are the many types of it?
2.23.
23. In a table, what is the DEFAULT option?
2.24.
24. Differentiate between Truncate and Delete?
2.25.
25. Define constraints and their types.
2.26.
26. How many memory layers does Oracle shared pool have?
2.27.
27. Define Discard File.
2.28.
28. Where are global variables declared in Oracle?
2.29.
29. In Oracle, what do you mean by recursive hints?
2.30.
30. Explain Oracle’s RAW Datatype.
2.31.
31. What are the many sorts of Oracle form modules?
2.32.
32. Describe the data type of the dual table.
2.33.
33. What are the differences between Primary Key and Unique Key?
2.34.
34. What are recursive hints in Oracle?
2.35.
35. What limitations do DML operations on Views have?
3.
Frequently Asked Questions
3.1.
What's the most efficient technique to get data from a table?
3.2.
What does a Candidate Key entail?
3.3.
Define the attributes of the Cursor.
4.
Conclusion
Last Updated: Jun 14, 2024

Oracle Interview Questions

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About Oracle

Oracle is one of America's largest global computer technology businesses, with headquarters in Austin, Texas. Oracle sells cloud-engineered solutions, Database software and technologies, and enterprise software, focusing on its database management systems.

Oracle is the second-largest software corporation in terms of sales and market capitalization. One of the critical reasons for Oracle's growing popularity in the IT business (its high-quality products) is its great work culture and ideals. As a software developer, you want to strike a healthy work-life balance, and Oracle is known for it.

We have collected many Oracle interview questions. These questions will help you crack the Oracle interview and land your dream job. The following section will discuss some of the most common oracle interview questions. These interview questions will also help in understanding various concepts of Oracle.

Top Oracle Interview Questions

1. Using which language is the Oracle database developed?

It is developed using the C language.

2. What is tablespace with respect to the Oracle database?

It is the logical storage unit of an Oracle database. It's not more than a collection of linked logical structures. Data is logically saved in Oracle tablespaces and physically saved in data files associated with those tablespaces.

3. Define the Oracle table.

It is the basic unit of data storage in Oracle. It has rows and columns which store all the accessible data.

4. Give uses of a control file.

The uses of the control file are

  • Recovery of the database
  • The control file identifies the database and redo log files that must be opened for database operations to occur when an ORACLE database instance is launched.

5. Differentiate between VARCHAR & VARCHAR2?

The Oracle data type Varchar and Varchar2 are used to store variable-length character strings. 

To highlight the significant distinctions between them, check the table below-

6. Differentiate between a hot and cold backup in Oracle and tell about their benefits.

HOT Backup:

It is performed while the database is live; a hot backup is also called as an online backup. Some websites can't shut down their databases while performing backups since they are in use 24 hours a day, seven days a week.

COLD Backup:

If the database is shut down using the SHUTDOWN normal command, a cold backup (also known as an offline backup) is done. If a database is suddenly shut down due to an unknown condition, it should be reopened in RESTRICT mode before being shut down with the NORMAL option.

For a complete cold backup, the following files must be backed up.

All data files, control files, online redo log files (optional), and the init.ora files are required.

7. Define various Oracle database objects.

The following is a list of Oracle database objects and their descriptions:

Tables: Tables are a collection of items arranged vertically and horizontally.

Tablespaces: In Oracle, a tablespace is a logical storage unit.

Views: It is a virtual table that has been created by combining data from one or more tables.

Indexes: Indexes are a performance-tuning technique for processing records.

Synonyms: Tables have names that are synonyms.

8. Define COALESCE function?

It is used to return the value in the list that is set to be not null. It will return NULL if all of the values in the list are null.

Coalesce(value1, value2, value3,value4 ,…)

9. Tell about the various constraints in Oracle.

NULL: It denotes that a column may contain NULL values.

NOT NULL: This specifies that a column cannot have any NULL values.

CHECK:  Verify that the values in the supplied column fulfill the specified requirements.

DEFAULT:  This indicates that the value has been set to the default value.

10. Describe the Redo Log file mirroring?

  • Mirroring is the process of having a copy of redo log files.
  • It's accomplished by putting together a collection of log files. This guarantees that LGWR sends them to all members of the current on-line redo log group automatically.
  • In the event that one of the groups fails, the database will immediately transition to the next group. It has a negative impact on performance.        

11. Differentiate between SQL and iSQL*Plus?

The following table shows the difference between SQL and iSQL*Plus:

12. In SQL queries, what is the purpose of the double ampersand (&&)? Could you give an example?

If you wish to reuse the variable value without having to prompt the user each time, use "&&."

For ex: 

Select stuid, sname, && column_name from student order by &column_name;

13. Describe the temporal data types in Oracle.

Oracle supports the temporal data types listed below-

Date Data Type: Various Date Formats

TimeStamp Data Type: Various Time Stamp Formats

Interval Data Type: The time between two dates.

14. Write code to display row numbers with records.

The format will be:

Select rowno, <fieldnames> from table;

This query will return row numbers and field values from the specified table.

15. Describe the save point in the Oracle database.

Save points are used to divide a large transaction into smaller portions. It allows for the reversal of a transaction. A total of five save points are allowed. It's also where we save our data; if something goes wrong, you can go back to where you saved your SAVEPOINT.

16. Differentiate between PL SQL and SQL?

The following table shows the difference between SQL and PL/SQL:


17. Describe the order of precedence which is used in executing SQL statements?

The following table shows the order of precedence which is used in executing SQL statements:

18. Describe the uses of ANALYZE command.

The ANALYZE command is used to perform the following functions on an index, table, or cluster:

- It helps in the dentification of migrated and chained table or cluster rows.

- It facilitates validating the object's structure.

- It aids in the collection of statistics about the optimizer's objects. After that, they're saved in the data dictionary.

- It aids in the deletion of object statistics from the data dictionary.

19. Explain about types of snapshots.

Snapshots are divided into two categories:

Simple snapshots - based on a query without GROUP BY clauses, CONNECT BY clauses, JOINs, sub-queries, or operations snapshots.

Complex snapshots, which include at least one of the preceding.

20. What is the definition of a transaction? Describe the most common errors that can occur during the execution of any transaction.

A transaction is a logical unit of work comprising a collection of DML statements. The following are some common errors that can occur during the execution of any transaction:

  • Constraints are being broken.
  • Mismatch in data types.
  • The value is too large for the column.
  • The server goes down, or the system crashes.
  • The session was a complete failure.
  • The process of locking takes place.

21. In Oracle, what is a bulk copy or BCP?

Bulk copy, often known as BCP in Oracle, is a method of importing or exporting data from tables and views without copying the data's structure. The key benefit of BCP is that it has a quick process for copying data and that you can quickly backup your data.

22. In SQL, what is locking? What are the many types of it?

Concurrent transactions can't interact destructively if they're locked. Locks remained in place until Commit or Rollback was performed. The following are examples of locking mechanisms:

Implicit Locking: Except for SELECT, all SQL statements are subject to implicit locking.

Explicit Locking: This can be done explicitly by the user.

In addition, there are two locking options:

Exclusive: Other users can't utilize it because it's exclusive.

Share: Allows other users to see what you're working on.

23. In a table, what is the DEFAULT option?

The DEFAULT option can be used to set a default value for a column. If a row is added without a value for a column, this option prevents null values from entering the column. The value of the DEFAULT column can be a literal, an expression, or a SQL function like SYSDATE or USER, but it can't be the name of another column or a pseudo column like NEXTVAL or CURRVAL.

24. Differentiate between Truncate and Delete?

The main difference between Truncate and Delete is as below:

25. Define constraints and their types.

If there are dependencies, constraints are employed to prevent improper data entry or deletion. At the table level, constraints impose rules. Constraints can be added to a table simultaneously as the table or after it has been built. At the column or table level, constraints can be defined. The USER-CONSTRAINTS data dictionary table can be used to see the constraints defined for a certain table. Except for NOT NULL, which can only be defined at the column level, any constraint can be defined at the table level. There are five different sorts of constraints:

  • Not Null Constraint
  • Unique Key Constraint
  • Primary Key Constraint
  • Foreign Key Constraint
  • Check Key Constraint.

26. How many memory layers does Oracle shared pool have?

There are two layers in Oracle shared pools:

  • Data dictionary 
  • Cache library cache

 

27. Define Discard File.

It is as follows:

  • .dsc is the file extension.
  • Using the discard file clause, we must provide the discard file within the control file.
  • The discard file additionally stores reflected records based on the control file's when clause condition. In the table clause, this condition must be met.

28. Where are global variables declared in Oracle?

We only declare global variables in Oracle's Package Specification.

29. In Oracle, what do you mean by recursive hints?

The number of times a dictionary table is continually called by various processes can be defined as a recursive hint. The tiny size of the data dictionary cache causes recursive hints.

30. Explain Oracle’s RAW Datatype.

Variable-length binary data or byte string values are stored in Oracle using the RAW datatype. A raw's maximum size in a particular table is 32767 bytes.

It's easy to get mixed up on when to use RAW, varchar, and varchar2. Let me highlight the fundamental distinctions between them. When RAW data is transmitted to various systems, PL/SQL can not recognize the data type and cannot do any conversions. This type of data can only be queried or added to a table.

31. What are the many sorts of Oracle form modules?

The following are the many Oracle form modules:

  • Menu module
  • Pl/SQL Library module
  • Form module
  • Object Library module

32. Describe the data type of the dual table.

In an Oracle database, the DUAL table is a one-column table. DUMMY is a single VARCHAR2(1) column in the table with the value 'X’.

33. What are the differences between Primary Key and Unique Key?

The following table shows the difference between Primary Key and Unique Key:

34. What are recursive hints in Oracle?

The recursive hint refers to the number of times a dictionary table is called repeatedly by different processes. The small size of the data dictionary cache causes recursive hints.

35. What limitations do DML operations on Views have?

Some of the limitations of DML operations on Views:

If the View contains the following, you can't DELETE a row:

  • Group Functions
  • A Group By clause
  • The Distinct Keyword
  • The Pseudo column ROWNUM Keyword.

If a View contains the following, you won't be able to MODIFY data in it:

  • Group Functions
  • A Group By clause
  • The Distinct Keyword
  • The Pseudo column ROWNUM Keyword.
  • Columns defined by expressions (Ex; Marks * 50)
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Frequently Asked Questions

What's the most efficient technique to get data from a table?

Using ROWID in the SQL query is the easiest approach to get the data.

What does a Candidate Key entail?

Candidate Key refers to the columns in a table that can be used as a Primary Key.

Define the attributes of the Cursor.

In Oracle, each Cursor has properties that enable an application programme to test the Cursor's state. The properties can be used to see if the cursor is open or closed if found and to count the number of rows.

Conclusion

This article contains the basic Oracle interview questions for both freshers and experienced applicants. Check out Android interview questionspython interview questions, DataStage Interview Questions, and more to ace your interviews. Do upvote our blog to help other ninjas grow. 

We hope you were able to find answers to the most often requested Oracle Interview questions in this article. The solutions provided to the questions above are also helpful in learning the fundamentals of Oracle.

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