Oracle Interview Questions and Answers

The Hiring Process

Contrary to a majority of the younger tech companies, this old giant has a more traditional approach to interviewing. You won’t be bombed with fancy “motivational” questions. People, who spent years learning programming languages, are motivated per se. Oracle values that and concentrates on your technical knowledge.
Which must be brilliant. At first, they’ll look at your academic records. If these demonstrate a sufficient level and consistency, you’ll be invited to pass an online test. Next, you’ll go through a double round of technical interviews conducted in person. At last, you’ll talk with an HR manager.
A lot of the interviewees reported the technical part to be a tough and the most decisive one. In this article, we focused on the Oracle interview questions that guide you through this challenge.
Want to read more interviews? You will find more company related interviews that include Google, IBM, Apple, Microsoft, and others. Find all of them under the “Companies” category on our blog.

1. Logical tests

Oracle remains one of the leaders on the database solutions market. And a dream for many IT folks.
Most of the Oracle interview questions are centered around the popular querying language — SQL — and its Oracle extension.
But some questions will test your acumen, too. For instance, you may be asked to solve a Sudoku! Another time a candidate would have to explain the so-called 0-1 Knapsack Problem. Both exercises are about arranging things, optimizing processes, and getting out of the logical traps.
Keep your mind fit and do not focus too much on acquiring static knowledge. They want a person that can think quickly and extraordinarily. If you can do this, any new skills will stick to you without too much effort.

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2. SQL questions

The Oracle technology is built upon SQL. As a candidate, you have to be fluent in writing queries. You will be asked about all existing SQL operators and especially about differences between “synonymical” operators.
Do you remember, why “TRUNCATE” is not the same as “DELETE”? If not, hurry to refresh your SQL knowledge. Despite both commands erase data, they do it in a different manner and the consequences of the deletion are different.
As a developer, database administrator, or data scientist, you routinely write SQL queries. If you come from another professional field, you can catch up with your experienced competitors by finishing an online SQL course.

3. Advanced SQL questions

At Oracle, they also value details. Another popular question that a lot of candidates mention is the following.
What is the difference between the VARCHAR data type and the VARCHAR2 data type?
Previously, the second one would drop an empty string, whereas the first one will save the string as it is, including empty spaces. Currently, Oracle adjusted their behavior. Using one of the formats makes no difference, but Oracle recommends you not to save data in VARCHAR.
Using a wrong data type can ruin a lot of the treasured data. Imagine, you enter a product name like “red shoes for teenagers.” You have missing name fields for a few products. Then you want to sort your products by categories. Before this recent change, VARCHAR2 would not count products with no name. You would have a mismatch between the number of the products and the same number calculated as a sum of products in different categories.

4. PL/SQL questions

Even if you can prove an experience in working with Oracle and SQL databases, the interviewer will ask you to list major differences between the two.
PL/SQL is a procedural extension of SQL. Roughly speaking, it can do more things than SQL can. It possesses some abilities of the so-called high languages. With PL/SQL you can write conditional and looping statements.
But the main advantage of PL/SQL is its way of handling single queries. SQL will send several statements to the server one by one, thus increasing the processing time enormously. PL/SQL will send a complete query and won’t make a user wait for a result for ages.

5. Data types in PL/SQL

Before the Oracle recruiters will grant you access for writing queries for them, more proof for your qualification needs to be delivered. In addition to the fluency in PL/SQL commands, you need to know all data types. Storing data in the right format prevents confusion and losing important information.
As a database specialist at Oracle, you must be able to make the right decision about data types to use. If you save dates in numeric format, single digits will be summed up and converted to a number. Besides, PL/SQL has a few very specific data formats.
Each format allows only particular manipulations with the data.

6. What are expressions?

By listing a few examples of expressions, you have a chance to confirm your exceptional knowledge of the data types.
Expressions are basically statements that either transform data or data format.
An expression can calculate a sum, check if a string is present in another string, and so on. Each combination of operators and operands is an expression.
Even 1 + 1 is an expression! An expression must make sense. Otherwise, you are not getting the job. 1 + “st” will result in an error, but “1” || “st” will output “1st”.
Operators, commands, and data types do not exist separately from each other. They build a meaningful system.

7. Cursors, triggers and constraints

Till now, you could have managed through the Oracle interview questions with only SQL and general programming knowledge. But this part will test that you are really familiar with the Oracle technologies.
All three terms are native to PL/SQL. Cursors are mechanisms to fetch more than one row from a database. Triggers are programs and constraints are rules. In particular, triggers are starting points for actions to be performed in a database. Triggers are active when specific events happen.
When a user logs in into a database, this is an event. Consequently, when a connection to the database is being closed, an event triggers fires, too.

8. Transaction specifications in PL/SQL

You cannot immediately change anything in an Oracle database. The changes are stored in the buffer. To apply them to the database, or even to stop the implementation of such changes, you deploy three basic statements.
Those are COMMIT, ROLLBACK, and SAVEPOINT. Make sure you understand their usage well. The first one will finalize your changes. The second one is your “Undo” button. The third one makes a snapshot to let you get back to the last status quo you need.
These three statements are inherited SQL ones.

9. Handling exceptions

For whatever reason, a PL/SQL script can fail. You do not want to let the process just abort without a notice or an alternative result. To prevent undesirable consequences like these, you can implement an exception handling into your script.
By this, you just tell a program what to do, if it fails to perform the original script. It can throw a message to give you a clue, why the run was not successful.
A typical error would be a failure to fetch any data. For this case, and for nine additional ones, Oracle offers predefined exceptions. For any specific errors, you can create your own ones.

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10. Write a PL/SQL script

You are now one step away from your dream. But your interviewers want the supreme proof of your skills. A practical test.
You will need to write a script that creates something like a sequence of numbers. The result must align with a few particular rules that you have to take into account in the script. With the right order and the right syntax.
If you had little to no practical experience with the Oracle language, you should definitely take a learning course. Some providers offer a certification that can be your pass into the Oracle world. Consider it seriously, if you do not have sufficient experience in the field.

11. Advanced Oracle questions

To apply for a non-beginner job, you’ll need to be able to build Oracle forms and reports. You create them for the end users, so that they do not need to write any queries. Users will just click some buttons, like in any other usual application.
Reports are summaries presented to the users.
Another important bunch of advanced Oracle interview questions refers to the so-called Performance Tuning. It includes different measures aimed to accelerate the execution of the database actions.
A database performance depends on the database design. It must be simple and straightforward. You need to know the principles of an efficient database design, like avoiding redundant or duplicate data.

12. Oracle ecosystem: apps and architecture

Oracle builds all applications following the same scheme and the same philosophy. It stands for minimalistic and thorough software architecture. The company supposes that every future employee understands and shares this spirit.
Your interviewers may expect you to be familiar with a wide range of Oracle products. At least, you should understand the basic market niche and the software landscape.
One group of the most popular Oracle applications are enterprise resource planning (ERP) systems. An ERP consists of a database, an application, and a user interface. Opposite to its many competitors, an Oracle ERP uses one single database, whereas a typical ERP architecture would include a few of them.
As a successful candidate, you should know the main Oracle’s USPs and their technical background. With this last knowledge, you are absolutely fit for the ultimate list of the Oracle interview questions.

Final Notes

Oracle wants to ensure that their databases will be in safe hands. That’s why most of the Oracle interview questions are in-depth technical ones.
People who possess a structured and systematic way of thinking — and some practical knowledge, of course! — would not have any difficulties to answer them.
And if you have read our Oracle guide, you know what to expect.
Why no teamwork questions at all? Keep in mind, Oracle was founded in … 1977! It is still one year younger than Apple and two years younger than Microsoft. Compared to its coverage, Oracles has not earned a reputation for being a dynamic and innovative working place. It is rather a conformist company from the golden age of big corporations.
Oracle tends to have clearly structured working routines. Your responsibilities will be fixed and aligned with the team goals. This way of working requires less coordination. The probability of conflicts is low.
If you love your work and you are a good technician, you will be welcomed there. As a price, you’ll have to express your creativity outside of the job.