Top 40 Oracle PL/SQL Interview Questions and Answers

Oracle PL/SQL developers are still in high demand, especially in sectors like banking, insurance, and healthcare that rely significantly on Oracle databases. Despite the emergence of newer technologies, PL/SQL remains a useful skill because of its close integration with the Oracle database and its capacity to effectively handle intricate data processing tasks. Here are the top 40 Oracle PL/SQL interview questions and answers to help you ace your next interviews confidently. Explore our Oracle PL/SQL course syllabus.

Oracle PLSQL Developer Interview Questions for Freshers

Here are the basic interview questions for PLSQL freshers:

1. What is PL/SQL?  

Oracle’s exclusive procedural extension for SQL is called PL/SQL (Procedural Language/Structured Query Language). It enables you to compose code blocks that incorporate procedural elements like loops, conditional statements, and exception handling with SQL statements.

2. What are the advantages of using PL/SQL?  

Some of the advantages of using PL/SQL are:

• Performance: Database processing reduces network traffic.
• Data Integrity: Upholds database-level business rules.
• Security: Provides more precise control over who can access data.
• Maintainability: Using functions and procedures to create modular code.
• Portability: Operates on any Oracle-compatible platform.

Recommended: Oracle SQL Course Syllabus

3. What are the different types of PL/SQL blocks?  

There are three types of PL/SQL blocks:

Anonymous blocks: One-time execution blocks without names.

Named Blocks with names include triggers, types, packages, functions, and procedures.

Subprograms are routines and procedures that other PL/SQL code can call.

4. Write the basic structure of a PL/SQL block.

DECLARE  — Optional: Declarations of variables, types, and cursors

BEGIN    — Executable statements

    — SQL statements, procedural logic, exception handling

EXCEPTION — Optional: Exception handlers

    — Code to handle errors

END;      — End of the block

5. What are variables in PL/SQL?

In PL/SQL, a variable is a place to store a value of a particular data type. It is a term used to describe a temporary storage space that programs can control.

How to use PL/SQL variables:

• Before utilizing a variable, declare it in the block’s declaration section.
• Give the variable a name and indicate what kind of data it contains.
• You can choose to set the variable’s initial value to its default value.  

6. What are the rules for PL/SQL variables?

The rules for PL/SQL variables:

• Variable names need to be legitimate and no more than thirty characters long.
• Variable names have to begin with an ASCII letter and finish with a dollar sign, underscore, or number.
• There is no case sensitivity in variable names.
• It is not possible to utilize reserved PL/SQL keywords as variable names. 

7. What are the advantages of using variables in PL/SQL?

Advantages of PL/SQL variable usage

• In PL/SQL programs, variables facilitate data manipulation.
• Procedures and functions can receive input and output values from variables.
• The data types of existing columns, rows, or cursors can be matched using variables. 

8. What are the different data types available in PL/SQL?

Numerous data types are supported by PL/SQL, including:

• NUMBER (numeric)
• VARCHAR2 (variable-length string)
• DATE (date and time)
• BOOLEAN (true/false)
• PLS_INTEGER (integer, faster than NUMBER)
• RECORD (composite data type)
• TABLE (collection type)

9. What are cursors in PL/SQL?

A named control structure known as a cursor in PL/SQL enables an application to choose and get data from a result set one row at a time. Both explicit and implicit cursors are possible.

• In a result set, a cursor serves as a pointer to the current row.
• The result set has a forward and backward moving cursor.
• A context area, which houses the data required to process a SQL statement, is linked to a cursor.
• The active set is the collection of rows that a cursor is currently holding. 

10. What are the different types of cursors?

The various types of cursors:

Implicit cursors: Oracle automatically creates implicit cursors for single-row queries.

Explicit cursors: For multi-row queries, the programmer defines explicit cursors, which give the user more control.

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11. What are the attributes of a cursor?

Information regarding the state of the cursor is provided by its attributes:

• %FOUND: Boolean; if a row was fetched, it is true.
• %NOTFOUND: If no record was retrieved, the Boolean value %NOTFOUND is true.
• %ROWCOUNT: Number of rows retrieved.
• %ISOPEN: If the cursor is open, this Boolean value is true.

12. What is the difference between a procedure and a function?

A function performs a calculation or operation and returns a specific value to the calling code, whereas a procedure carries out a series of actions without returning a value. In other words, a function “computes” a result, whereas a procedure merely “does something.”  

• Return value: Unlike procedures, which do not necessarily return a value after execution, functions do.
• Purpose: While a procedure is used to carry out a sequence of actions to complete a task, a function is usually utilized when a specific result needs to be calculated depending on input values. 

Examples:

Function: To determine a circle’s area, a function would accept its radius as input and output the area as a value.

Procedure: To print a greeting on the screen, a procedure would just show the message without giving back any particular value.  

13. What are packages in PL/SQL?

Schema items known as packages are used to organize related variables, constants, types, functions, and procedures. They offer enhanced performance, encapsulation, and modularity.

14. What are the benefits of using packages?

Some of the advantages using packages in PL/SQL:

• Modularity: Group related code together.
• Encapsulation: Keep the specifics of implementation hidden.
• Name Space Management: Steer clear of name disputes.
• Performance: Only one load of a package is made into memory.

15. What are triggers in PL/SQL?

A named database object that initiates a series of operations in response to a particular event is known as a PL/SQL trigger. When database events like inserts, updates, or deletions occur, triggers are used to automate responses.  

16. How do triggers work? 

• Triggers can be turned on or off and are kept in the database.
• The database automatically runs a trigger that has been enabled when the triggering event takes place.
• Tables, views, schemas, and the database itself can all have triggers written for them.
• Triggers can be used to generate virtual column values, log events, or collect data, among other tasks.

17. How to create a trigger? 

• Make use of the CREATE TRIGGER command in PL/SQL.
• Give the name of the trigger, the event that triggers it, and the action that triggers it. 

Examples:

DML Triggers: DML commands like INSERT, UPDATE, and DELETE cause these triggers to be produced on tables or views.  

Startup Triggers: These triggers can be used to carry out setup operations and become active upon database initialization.

18. What are the different types of triggers?

The various types of triggers:

• Statement-level triggers: Each triggering statement causes one fire.
• Row-level triggers: They only need to fire once for every row that the triggering statement affects.
• Before/after triggers: Triggers that occur before or after the triggering event are known as before/after triggers.
• Insert, update, and delete triggers: Set off in response to particular DML activities.

19. What is an exception in PL/SQL?

An exception in PL/SQL is an error circumstance that arises while a program is running. The user or the runtime system can define exceptions. 

20. What are the types of exceptions?

The various types of exceptions are:

• System-defined exceptions: When an error is detected, the runtime system raises these. For instance, when there is a division by zero or when memory runs out, the ZERO_DIVIDE and STORAGE_ERROR exceptions are produced. 
• User-defined exceptions: The programmer of a particular application defines these. To signify an overdrawn bank account, for instance, a programmer can define an exception named insufficient_funds.

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Oracle PLSQL Interview Questions for Experienced Candidates

Here are the popularly asked interview questions for Oracle PL SQL developer

1. How do you handle exceptions in PL/SQL?

Programmers employ exception handlers to deal with exceptions. Exception handlers are distinct programs designed to deal with exceptions that are raised. Following the execution of an exception handler, the enclosing block resumes and the current block ceases execution.

To deal with certain exceptions, utilize the EXCEPTION block in conjunction with WHEN clauses. To capture any unhandled exceptions, you may also utilize OTHERS.

2. What is a REF CURSOR?

An Oracle database result set can be accessed using a PL/SQL data type called a REF CURSOR. Large volumes of data can be transferred using it as a handle or pointer to a query result set.  

3. What are collections in PL/SQL?

Multiple components of the same data type can be stored in collections, which are data structures. Types consist of:

• Index-by tables (Associative arrays): Indexed by string or number.
• Nested tables: Table within a table.
• VARRAYs: Fixed-size arrays.

4. What is dynamic SQL in PL/SQL?

SQL statements that are created and run at runtime are referred to as dynamic SQL. Static is the antithesis of dynamic. SQL statements that are fully described, or fixed, at the time the code containing them is compiled are referred to as static SQL (sometimes called embedded SQL).

5. What are some methods for executing dynamic SQL?

Some of the methods to execute dynamic SQL:

EXECUTE IMMEDIATE

OPEN … FOR … USING (for REF CURSORS)

DBMS_SQL package (for more complex scenarios)

6. What are bind variables and why are they important in dynamic SQL?

In dynamic SQL queries, bind variables are placeholders that are changed to their actual values during runtime. By enabling Oracle to reuse the execution plan, they enhance performance and stop SQL injection issues.

7. What is the difference between COMMIT and ROLLBACK?

COMMIT: Stores every modification made to the active transaction.

ROLLBACK: All modifications made to the current transaction since the last commit are undone by rolling back.

8. What is an autonomous transaction?

A transaction that can be committed or rolled back independently from the primary transaction is known as an autonomous transaction. It makes it possible to perform particular tasks without interfering with the primary transaction.

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9. What are some performance tuning techniques in PL/SQL?

Some of the performance tuning techniques in PL/SQL:

• Make use of bind variables.
• Reduce the number of network round trips.
• Make use of bulk processing (BULK COLLECT, FORALL).
• Make SQL queries more efficient.
• Make use of the right data types.
• Use Explain Plan to analyze and fine-tune SQL statements.

10. Write a PL/SQL block to calculate the factorial of a given number.

The PL/SQL block to calculate the factorial of a given number:

DECLARE

a NUMBER := 4;

f NUMBER := 1;

BEGIN

while(a>0) loop

f:=f*a;

a:=a-1;

end loop;

dbms_output.put_line(‘Factorial is ‘|| f);

end;

11. Write a PL/SQL procedure to insert data into a table.

The PL/SQL procedure to insert data into a table:

CREATE TABLE employees (

    employee_id INT,

    first_name VARCHAR(50),

    last_name VARCHAR(50),

    department VARCHAR(50)

);

INSERT INTO employees (employee_id, first_name, last_name, department)

VALUES (101, ‘John’, ‘Doe’, ‘Sales’);

12. Write a PL/SQL function to return the salary of an employee given their employee ID. 

CREATE OR REPLACE FUNCTION get_employee_salary (p_employee_id IN employees.employee_id%TYPE)

  RETURN employees.salary%TYPE

IS

  v_salary employees.salary%TYPE;

BEGIN

  SELECT salary

  INTO v_salary

  FROM employees

  WHERE employee_id = p_employee_id;

  RETURN v_salary;

EXCEPTION

  WHEN NO_DATA_FOUND THEN

    — Handle the case where the employee ID is not found.  You could:

    — 1. Return a default value (e.g., 0, -1)

    — 2. Raise an application-specific exception

    — 3. Return NULL (which might be appropriate depending on your needs)

    — Example 1 (Return a default value):

    RETURN 0;

    — Example 2 (Raise an exception – better practice):

    — RAISE_APPLICATION_ERROR(-20001, ‘Employee ID not found.’);  — Customize error code and message

    — RETURN NULL; — If you still want to return null after raising the exception.

    — Example 3 (Return NULL):

    — RETURN NULL;

  WHEN TOO_MANY_ROWS THEN

    — Handle the unlikely case where multiple employees have the same ID.

    — In a properly designed database, this shouldn’t happen.

    RAISE_APPLICATION_ERROR(-20002, ‘Multiple employees found with the same ID.’);

    RETURN NULL; — Or handle as you see fit.

  WHEN OTHERS THEN

    — Handle any other unexpected exceptions.  Log the error for debugging.

    DBMS_OUTPUT.PUT_LINE(‘Error in get_employee_salary: ‘ || SQLERRM);  — Log the error

    RAISE_APPLICATION_ERROR(-20003, ‘An unexpected error occurred.’); — Or return NULL

    RETURN NULL;

END;

/

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13. Explain how you would use a cursor to process all rows in a table.

Steps to use a cursor to process all rows in a table:

Step 1: Declare the cursor:

• To specify the SELECT query that will retrieve the data you wish to process, use a DECLARE CURSOR statement.
• Usually, variables are also included in this expression to hold the values from each fetched row.

Step 2: Open the cursor:

• To make the result set available and to move the pointer, execute an OPEN statement.

Step 3: Fetch rows within a loop:

• To assign the values to the stated variables, fetch one row at a time from the cursor using a FETCH statement inside a loop.
• Typically, the loop condition determines whether more rows need to be fetched (for example, while FETCH_STATUS = 0). 

Step 4: Perform operations on each row:

• Use the variables to retrieve the data from the fetched row inside the loop, then carry out the necessary operations (updates, calculations, etc.). 

Step 5: Close the cursor:

• Use a CLOSE statement to release the cursor once all rows have been processed. 

PL/SQL Block to process all rows in a table:

DECLARE customer_cursor CURSOR FOR 

SELECT CustomerID, CustomerName, OrderTotal FROM Customers;

OPEN customer_cursor;

FETCH NEXT FROM customer_cursor INTO @customerID, @customerName, @orderTotal;

WHILE @@FETCH_STATUS = 0

BEGIN

    — Perform operations on the fetched customer data

    PRINT ‘Customer ID: ‘ + CAST(@customerID AS VARCHAR) + ‘, Name: ‘ + @customerName;

    FETCH NEXT FROM customer_cursor INTO @customerID, @customerName, @orderTotal;

END

CLOSE customer_cursor;

DEALLOCATE customer_cursor;

14. Describe a scenario where you would use a trigger.

There are scenarios like below we could use a trigger:

• Data consistency: By automatically carrying out tasks when particular events occur in the database, such as updating related entries or verifying data before it is saved, triggers are helpful for upholding data integrity and enforcing business standards.
• Logging and auditing: You can create an audit trail to monitor data changes and spot possible problems by setting up triggers to record adjustments to significant tables.
• Cascading actions: Triggers can be used to link operations together if you need to carry out several tasks in response to a single change. This will guarantee that all required updates are carried out in the right order.  

Real-Time Use cases of Triggers:

• Inventory management: A trigger can automatically adjust inventory levels to match a product’s sale.
• Account management: A trigger may automatically construct a default contact record for a newly established account.
• Price updates: A trigger could adjust the price of any pending orders that contain a product if its price changes.
• Security checks: To avoid unwanted access, a trigger could be used to confirm user authorization prior to a sensitive data update.  

15. How to use a package and list some scenarios.

By encapsulating logic that belongs together under a single name and making it accessible to other areas of your application while preserving a clear structure and separation of concerns, a package aggregates a group of related procedures and functions into a single unit, improving code organization, reusability, and management. 

To use a package, following will be utilized:

• Package Specification: This section outlines the package’s public interface, including the names and specifications of the functions and processes that are accessible from outside the package.
• Package Body: This section includes any internal helper functions or private variables as well as the actual implementation details of the processes and functions specified in the specification.  

Example Scenarios of using a Package:

Consider creating a database application to handle client data. A package called “CustomerManagement” might be made that has steps for:

• To add a new customer record, use the CreateCustomer function.
• UpdateCustomerDetails: To change current customer information
• To get rid of a customer record, use DeleteCustomer.
• GetCustomerInfo: This function retrieves customer data by using an ID.

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16. Write the PL/SQL block to demonstrate FORALL and BULK COLLECT.

DECLARE

  TYPE emp_rec_type IS RECORD (

    employee_id employees.employee_id%TYPE,

    new_salary employees.salary%TYPE

  );

  TYPE emp_rec_table IS TABLE OF emp_rec_type INDEX BY PLS_INTEGER;

  emp_rec_array emp_rec_table;

BEGIN

  — 1. Fetch data into a collection using BULK COLLECT

  SELECT employee_id, salary * 1.1  — Example: Increase salary by 10%

  BULK COLLECT INTO emp_rec_array

  FROM employees

  WHERE department_id = 10;

  — 2. Update the employees table using FORALL

  FORALL i IN 1..emp_rec_array.COUNT

    UPDATE employees

    SET salary = emp_rec_array(i).new_salary

    WHERE employee_id = emp_rec_array(i).employee_id;

  COMMIT;  — Important: Commit the changes

  DBMS_OUTPUT.PUT_LINE(‘Number of employees updated: ‘ || SQL%ROWCOUNT);

EXCEPTION

  WHEN OTHERS THEN

    DBMS_OUTPUT.PUT_LINE(‘Error: ‘ || SQLERRM);

    ROLLBACK;  — Rollback on error

END;

/

17. When would you use dynamic SQL?

A potent PL/SQL approach that lets you create and run SQL statements at runtime is called dynamic SQL. When the SQL query’s content or structure is unknown until the program is running, this is crucial. 

In the following typical situations, dynamic SQL is required:

• Unknown table or column names that include data-driven applications and meta-driven processes.
• Variable WHERE clause conditions such as search functionality and filtering data.
• Building SQL statements programmability like generating complex queries and executing DDL statements.
• Handling a varying number of parameters such as stored procedures with optional parameters.
• Executing SQL statements from external sources like importing SQL scripts.

Example for Search Functionality:

CREATE OR REPLACE PROCEDURE search_employees (

  p_search_column IN VARCHAR2,

  p_search_value IN VARCHAR2

)

IS

  v_sql VARCHAR2(2000);

  v_count NUMBER;

BEGIN

  v_sql := ‘SELECT COUNT(*) FROM employees WHERE ‘ || p_search_column || ‘ = :1’;

  — Using EXECUTE IMMEDIATE with bind variable

  EXECUTE IMMEDIATE v_sql INTO v_count USING p_search_value;

  DBMS_OUTPUT.PUT_LINE(‘Number of matching employees: ‘ || v_count);

EXCEPTION

  WHEN OTHERS THEN

    DBMS_OUTPUT.PUT_LINE(‘Error: ‘ || SQLERRM);

END;

/

— Example usage:

EXECUTE search_employees(‘last_name’, ‘Smith’);

EXECUTE search_employees(‘department_id’, ’10’);

18. Explain the difference between a stored procedure and an anonymous block.

Although anonymous blocks and stored procedures are both essential PL/SQL building blocks, there are some significant distinctions between them that affect when and how you use them. Here are the differences:

Example:

— Stored Procedure (for calculating employee bonus)

CREATE OR REPLACE PROCEDURE calculate_bonus (p_employee_id IN employees.employee_id%TYPE)

IS

  v_salary employees.salary%TYPE;

  v_bonus NUMBER;

BEGIN

  SELECT salary INTO v_salary FROM employees WHERE employee_id = p_employee_id;

  v_bonus := v_salary * 0.10; — 10% bonus

  DBMS_OUTPUT.PUT_LINE(‘Bonus for employee ‘ || p_employee_id || ‘: ‘ || v_bonus);

END;

/

— Anonymous Block (for testing the procedure)

DECLARE

  v_emp_id employees.employee_id%TYPE := 100; — Example employee ID

BEGIN

  calculate_bonus(v_emp_id);

END;

/

When to use which:

• Use a stored procedure: When you have PL/SQL code that needs to be reused across several sections of your program, or when you need to encapsulate intricate logic and give it a straightforward interface, utilize a stored procedure.
• Use an anonymous block: When you have a one-time action that doesn’t require database storage or when you need to rapidly test a section of PL/SQL code, use an anonymous block.

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19. How do you implement security in PL/SQL?

To safeguard your data and apps, PL/SQL security uses a number of layers and recommended practices. Here are some security practices in PL/SQL:

• Least Privilege Principle such as granting only necessary privileges and Principle of least privilege applied to stored procedures.
• Object Privileges with queries like SELECT, INSERT, UPDATE, and DELETE, EXECUTE, and CREATE, ALTER, DROP.
• Roles by applying group privileges and implementing application rules.
• Stored Procedures and Functions (Security by Obscurity and Control) with encapsulation, input validation, and data masking within procedures.
• SQL Injection Prevention (Absolutely Essential) with binding variables and input sanitization.
• Network Security such as secure database connections and firewall protection.
• Regular Security Updates and Patching by staying up-to-date.
• Secure Coding Practices such as following secure coding guidelines and performing code reviews.
• Implementing data encryption techniques ((Transparent Data Encryption – TDE) like encrypt data at rest.
• Implementing Virtual Private Database (VPD) with row-level security practices.

20. Write a PL/SQL block for granting privileges through roles.

— Create a role

CREATE ROLE employee_role;

— Grant privileges to the role

GRANT SELECT ON employees TO employee_role;

GRANT EXECUTE ON get_employee_salary TO employee_role;  — Grant access to a stored function

— Grant the role to a user

GRANT employee_role TO john;

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Conclusion

Oracle PL/SQL interview preparation necessitates a thorough comprehension of both basic ideas and sophisticated methods. With these top 40 Oracle PLSQL interview questions and answers, you can show off your proficiency in this potent database programming language and approach your Oracle PL/SQL interview with confidence by fusing theoretical knowledge with real-world application. Enroll in our Oracle PL/SQL training in Chennai.