70 Common PL/SQL Interview Questions (And Example Answers)

Updated 9 July 2022

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In an interview for a programmer role, it is only natural to expect questions around your skill set. If your core competency is PL/SQL, changes are you used it extensively in database manipulations. Since PL/SQL is a vast subject, it would be useful to spend time and prepare in advance, with questions relevant to your experience. In this article, we examine some tips and a list of PL/SQL interview questions that can help you prepare.

Top 5 PL/SQL interview questions

When you prepare for a technical interview, refresh all relevant details about the language or skill. There may be questions related to fundamental concepts, advantages, drawbacks, troubleshooting and differences between commands and definitions. Here are five common PL/SQL interview questions and example answers:

1. What is PL/SQL?

When you are a programmer, the interviewer may expect you to have strong background knowledge of the language and its evolution, depending on your experience and skill level. Be prepared for such questions that allow you to demonstrate your expertise. Keep your answer brief with a couple of lines about PL/SQL's capabilities.

Example: "Designed and developed in the 1980s as a procedural language, PL/SQL is a variant of the powerful database program SQL. PL/SQL works as an SQL extension, and its syntax can contain SQL statements and enhance SQL capabilities. The Database server compiles PL/SQL program units and embeds the programming language along with the SQL and Java languages."

2. Explain some characteristics of PL/SQL?

An employer may expect a programmer to know the features of the language they code in. To code effectively in PL/SQL, you have to be familiar with its features and commands. Your interviewer may ask this question to assess your level of technical knowledge in PL/SQL.

Example: "PL/SQL is considered a portable coding language. This means that it lets you code on any operating system along with a range of programming structures. It supports object-oriented programming, structured programming, web application and server development. It also offers high-level security features."

3. What are some benefits of PL/SQL packages?

If you have a few years of experience and have worked on PL/SQL projects, your interviewer may ask this question. Along with coding, they may be keen to see if you have a clear understanding of the role of PL/SQL packages in application development. Give an example to explain how PL/SQL packages help improve the performance and functionality of large database systems.

Example: "You can use a PL/SQL package to store all related functions and procedures in one unit. It allows the memory to load multiple objects and allows all the code blocks to run simultaneously while reducing traffic. Both these factors help improve performance. With a PL/SQL package, developers can implement the object-oriented design in a top-down fashion. They can create the interface by referring to hidden code in the PL/SQL package. If you modify one module in a PL/SQL package, you can make similar changes in another."

4. What is the largest difficulty you faced in PL/SQL programming and how did you get past it?

If you are managing a team of PL/SQL programmers and have many years of work experience in PL/SQL, interviewers may ask you this question. It helps them to evaluate if you can get to the root cause of technical issues and overcome them. Talk about general issues and a couple of specific issues which you solved at work.

Example: "The biggest issue I faced in my last role as a PL/SQL programmer is that the PL/SQL code requires a database to function. At times, when my database went down, the code was no longer functional. I was the database administrator. To solve the problem, I focused on ensuring a high percentage of runtime by implementing monitoring and escalation software."

5. What is the command you use to get the privileges offered by Grant command?

The interviewer may ask more than one question like this, where the answer consists of a single word. It is important that you prepare for several questions like this. The interviewer can gauge your expertise based on the speed at which you answer such questions.

Example: "REVOKE."

Additional interview questions

These are some additional PL/SQL interview questions that you can prepare for:

Beginner interview questions

Interviewers may ask you these questions to test a basic understanding of PL/SQL:

Distinguish between SQL and PL/SQL.
Explain the features of PL/SQL.
What is meant by PL/SQL tables?
Can you explain the basic structure you follow in PL/SQL?
What is a PL/SQL package? What does it consist of?
Explain the PL/SQL compilation process.
What is exception handling in PL/SQL?
Explain joins and their types in PL/SQL.
List the triggers in PL/SQL.
What are the benefits of using triggers?
List the differences between Simple and Complex Views.
What are PL/SQL cursors?
Explain the cursor execution cycle.
Define Raise_Application_Error.
Write the code of a cursor for a loop.
Explain the process of writing comments in PL/SQL code.
What is NVL used for?
How is WHERE CURRENT useful?
When is the WHEN clause used in a trigger?
How would you differentiate between the cursors declared in procedures and those declared in package specifications?

Intermediate interview questions

Interviewers may ask you these questions to test an intermediate understanding of PL/SQL:

Give details of PL/SQL execution architecture.
What is the benefit of using SYSDATE and USER keywords?
State the differences between implicit and explicit cursors.
Compare a mutating table with a constraining table.
Explain two types of exceptions with some examples.
Why are SQLCODE and SQLERRM important and useful?
Explain the different character functions.
Define Intersect with an example.
What does ROWID do?
Distinguish between Anonymous block and sub-programs.
Why and when does a DECLARE become mandatory?
How are %TYPE and %ROWTYPE different? Explain with examples.
How are ROLLBACK and ROLLBACK different in PL/SQL?
What are set operators in PL/SQL?
Explain partitioning.
Create a PL/SQL script to display a series of numbers.
Explain actual and formal parameters.
What is an index? Explain the types of indices.
Write a PL/SQL program to check if a string of numbers is a palindrome.
Write a PL/SQL program to convert numbers into words.

Advanced interview questions

Interviewers may ask you these questions to test an advanced understanding of PL/SQL:

Where are pre_defined_functions located?
Describe Flashback Query.
Is there a way to find out if a column is indexed or not? Explain how.
Briefly talk about Rollback, Commit and Savepoint.
Compare Entity, Attribute and Tuple.
How do you debug PL/SQL code?
What is polymorphism in PL/SQL?
Explain in what contexts MERGE can be used.
Provide details of PLVtab, its uses and benefits.
List out differences between syntax and runtime error.
Compare and distinguish procedure, function and trigger.
Distinguish between triggers and constraints.
Briefly describe all types of constraints.
Describe SYSAL_DEPENDENCIES.
Create a query to find the top 5 highest-paid employees using ROW NUM.
What is the outcome of DML statement execution save, and why?
Explain a transaction and the possible errors that can occur while executing a transaction.
Distinguish between trim and delete collection methods.
Give a detailed explanation of Rank as an aggregate function with some examples.
Explain the differences between the operators Union and Union all.
Define subquery with an example.
Define correlated subquery with an example.
Compare NVL, NVL2 and Nullif.
Write a query to convert the system time into seconds.
Write a PL/SQL program to display all student names and their marks from a student table using %NOTFOUND attributes.

How do I prepare for a PL/SQL interview?

Whether you are a fresher or have a few years of experience, these tips can help you prepare for an interview:

Understand the job description. Read through the job description to understand the level of skill the employer is looking for. Apply only to those jobs where the company's expectations and your skills match.
Research the company. Research the company, their body of work, work culture and other relevant information. You can likely get this information from the company's website, social media accounts and press releases.
Make a PL/SQL question pool. Make a list of probable PL/SQL questions based on your learning and work experience or from fellow coders and internet platforms.
Practise answers. Once you have prepared a list of questions, practise saying the answers aloud to improve retention ahead of the interview.

Is PL/SQL difficult?

PL/SQL is often not difficult to understand for the individual who is interested in learning. An experienced programmer can understand the basics of PL/SQL in a couple of days. It may take you a few months to gain proficiency and knowledge to the level of an intermediate programmer. To become an expert, you may require extensive hands-on experience relating to a variety of projects.

Please note that none of the companies mentioned in this article are affiliated with Indeed.