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Top 20 Most Common Oracle Interview Questions

Technology is moving at a fast pace. And this holds especially true in the field of computer science and telecommunications with new software and its applications being constantly updated. As an IT professional this means that you must always be on your toes. And companies in this industry are always looking out for programmers who are well versed in the latest developments.

Regardless of your experience in the field-novice or expert- you can ace any interview you appear for. And to help you do that, here are the 15 of the most frequently asked Oracle interview questions and their answers.

1. What is the purpose of Oracle? And how does it work?

Oracle, or Oracle Database, is a Relational Data Base Management System (RDBMS). It is a software that is used to process, store, retrieve and manipulate data. It is based on PQ/SQL an extension over SQL (Structured Query Language).
Oracle works by making use of memory threads within the main memory system to analyze, manage and retrieve data.

2. In what ways can you write comments in Oracle?

For single statements, you can use two dashes (–).
For a block statement you can use (*–*).

3. What are Constraints and how can we use them?

Constraints are rules that you set up for your data.

They can be used either during table creation or later, to alter the table.

4. Is there a difference between Primary and Unique key?

A Primary key is used to identify a particular record in the data database there can be only on Primary key for a table and it must not hold a null value.

On the other hand, Unique key is used to avoid duplication of values in the system. There can be more than one Unique keys for a table and it is allowed to hold a null value.

5. How is TRANSLATE different from REPLACE?

You can use TRANSLATE when you want to replace characters one after another, while REPLACE allows you to replace an entire set of characters with a new complete string.

6. How do COALESCE and AGGREGATE differ?

COALESCE command returns the value in the table set to not null.
AGGREGATE command helps join the values of multiple records into a single value. For instance functions such as sum, average, and count.

7. What do you know about set operations in Oracle?

They are commands used to combine queries in order to receive unique results.
For example, INTERSECT will return the results common to every query executed. MINUS will allow you to obtain a result unique only to the first query. UNION and UNION ALL combine all the results obtained from all the queries, only that UNION ALL keeps the duplicate record.

8. How can we create a database trigger?

By the use of CREATE TRIGGER clause, a PL/SQL block can be created that will be set off automatically when the condition for it are met.

Also Read: 4 Tips to take your Career Forward while Staying in the Same Job

9. What is the purpose of Savepoints?

Much like in a video game, Savepoints are markers set up during programming. In case a particular transaction fails, we can return to the savepoint.

10. What are Errors and how do you deal with them?

They are exceptions that occur during programming and can be usually handled by using EXCEPTION block command.

11. What are Privileges and what is their purpose?

Privileges are granted access to another user’s data or the ability to execute a command.
They are used in creating roles and can be enabled and disabled for any user.

12. Is there a difference between Alias and Rename?

Yes, there is.
Rename is an invariable permanent name assigned to a record, while Alias is a temporary name.

13. What is View?

It is a logical table devoid of data, based on one or more different tables.

14. What is the use of Integrity Constraints?

These commands ensure the accuracy and consistency of data in the system. There are many types such as Domain Integrity, and Referential Integrity.

15. What are DECODE and CASE statements?

Both of the commands are used in the transformation of data values and work as alternatives to each other.

16. How do you merge two tables?

Data from different tables can be combined using MERGE command. It works by selecting and updating data in the source table and the second table respectively based on the query provided.

17. What is a Stored Procedure?

They are commands written for achieving a specific task that are saved and named as a group.

18. What is the function of the Index?

It is used to search for data within a database with efficiency.

19. What is Data Dictionary?

It is a set of read-only tables that contains metadata related to the information owned by a user.

20. What do you understand by Joins?

They are commands that can be used to collect data from several different tables having a common column.

Besides having a firm grasp on your subject, make it a point to listen to the interviewer carefully. Sometimes even the easiest questions can seem hard if you haven’t understood it.
Good luck!

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