Difference Between SQL and PL/SQL

When working with a database, two important terms that are encountered are SQL and PL/SQL. SQL is used for communicating with the database and performing operations. PL/SQL adds programming features and allows programmers to use loops, conditions, and variables for complex tasks. In this blog, you will learn the difference between SQL and PL/SQL with examples in detail.

Table of Contents:

• What is SQL?
• What is PL/SQL?
• Differences between SQL and PL/SQL
• Key Features of SQL
• Key Features of PL/SQL
• SQL vs PL/SQL Execution
  • Execution Flow in SQL
  • Execution Flow in PL/SQL
• Real-World Use Cases of SQL and PL/SQL
  • Real-World Use Cases of SQL
  • Real-World Use Cases of PL/SQL
• Conclusion

What is SQL?

SQL stands for Structured Query Language, a language used to communicate with databases. SQL is used to store, retrieve, update, and delete data in a database. SQL works with relational databases, which organize data into tables consisting of rows and columns. With SQL, you can ask the database to do things like get all of the information about customers, add another product, or change the price of an item. SQL is non-procedural, which helps you to simply tell the database what you want, without telling it how to do it. The database decides the best way to execute the task.

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What is PL/SQL?

PL/SQL stands for Procedural Language/Structured Query Language. It is an extension that was developed by Oracle, which allows you to create procedural code to use with databases. Unlike SQL, which only tells the database what to do, PL/SQL allows you to define how to do that process using programming concepts such as loops, conditions, and variables. PL/SQL is used to create blocks of code that can contain multiple SQL statements and control structures. The blocks allow you to execute complex operations within the database efficiently. PL/SQL is especially useful if you want to automate repetitive tasks, enforce business rules, or execute large operations with large amounts of data.

Differences between SQL and PL/SQL

Key Features of SQL

1. Data Querying: SQL helps you get and view specific data from tables using SELECT. You can also sort and filter the results.
2. Data Manipulation: You can add, update, or delete records in tables, making data management easy.
3. Data Definition: SQL lets you create, change, or remove tables and other database objects to organize your data.
4. Data Control: You can manage who can see or change data using commands like GRANT and REVOKE.
5. Transaction Management: SQL can run multiple operations as one unit, and you can save changes with COMMIT or undo them with ROLLBACK if something goes wrong.

Key Features of PL/SQL

1. Procedural Language: PL/SQL allows specifying the instructions with loops, conditions, and variables.
2. Code Blocks: Multiple SQL statements and the logic can be combined into a single block, which improves the execution of the query.
3. Variables and Constants: PL/SQL allows for storing temporary data in variables or constants for using them in calculations and controlling the program flow.
4. Error Handling: PL/SQL is capable of catching errors and handling them using an EXCEPTION block. This is very helpful to prevent the program from terminating unexpectedly.
5. Reusable Programs: You can create procedures, functions, and packages in PL/SQL, which makes it easy to reuse code for similar tasks.

SQL vs PL/SQL Execution

PL/SQL vs SQL Execution explains how SQL and PL/SQL run differently in a database. SQL executes one statement at a time, focusing mainly on data manipulation and retrieval. PL/SQL, on the other hand, allows execution of an entire block with multiple SQL statements and procedural logic, though each SQL command inside the block still runs individually. Understanding how these two modes of execution work is very important to select the best approach for different tasks. Let’s now understand how the execution takes place in SQL and PL/SQL.

Let’s create a sample table to understand the execution in SQL and PL/SQL

CREATE TABLE employees (
    emp_id INT PRIMARY KEY,
    emp_name VARCHAR(50),
    department VARCHAR(50),
    salary INT
);

-- Inserting sample data
INSERT INTO employees (emp_id, emp_name, department, salary) VALUES
(1, 'Amit', 'HR', 40000),
(2, 'Riya', 'Finance', 50000),
(3, 'Karan', 'IT', 60000),
(4, 'Sneha', 'HR', 45000),
(5, 'Vikram', 'IT', 70000),
(6, 'Anita', 'Finance', 52000),
(7, 'Arjun', 'IT', 75000),
(8, 'Meena', 'HR', 47000);

-- Display the inserted data
SELECT * FROM employees;

Output:

Execution Flow in SQL

Execution in SQL is simple. Each statement is sent to the database, executed, and the results are returned very fast. SQL does not group multiple commands. Instead, it executes one step at a time.

-- Increase the salary of HR employees
UPDATE employees 
SET salary = salary + 5000 
WHERE department = 'HR';

-- Fetch all employee records
SELECT * FROM employees;

Output:

Explanation: Here, the UPDATE query first increases the salary of HR employees, and the following SELECT query retrieves all employee records to show the updated data.

Execution Flow in PL/SQL

PL/SQL executes differently from SQL. Rather than executing one statement at a time, PL/SQL combines multiple SQL statements and programming logic inside a block. PL/SQL sends the entire block to the database server, which is then compiled and executed as a single unit. This added functionality makes PL/SQL even more powerful, since it allows you to use variables, loops, and conditions along with SQL statements all in one program.

Note: To display the output, ensure SET SERVEROUTPUT ON; is enabled in your SQL tool (such as SQL*Plus or SQL Developer).

Example:

DECLARE
    hr_count NUMBER;
BEGIN
    -- Count how many employees are in HR
    SELECT COUNT(*) INTO hr_count 
    FROM employees 
    WHERE department = 'HR';
    
    -- Display the result
    DBMS_OUTPUT.PUT_LINE('Number of employees in HR: ' || hr_count);

    -- Increase the salary of HR employees
    UPDATE employees
    SET salary = salary + 5000
    WHERE department = 'HR';

    DBMS_OUTPUT.PUT_LINE('Salaries updated for HR employees.');
END;
/

Output:

Explanation: Here, the PL/SQL block first counted the number of HR employees, next updated their salaries all at once, and finally displayed a confirmation message.

Real-World Use Cases of SQL and PL/SQL

SQL and PL/SQL are widely used across industries for managing data efficiently, with SQL helping in handling queries faster and PL/SQL simplifying complex business logic and automation.

Real-World Use Cases of SQL

1. Banking Software: Banks use SQL for rapid retrieval of data like account balances, transaction histories, or customer information when a user logs in to the online banking web application.

2. E-commerce Applications: E-commerce companies implement SQL to manage product lists, available stock, and customer orders.

3. Healthcare Management Software: Hospitals and clinics utilize SQL to store patient records, appointment schedules, and billing information.

Real-World Use Cases of PL/SQL

1. Payroll Processing: Companies utilize PL/SQL programs to determine employee wages, enforce tax rules, and create monthly payslips automatically.

2. Airline Reservation Systems: PL/SQL is a component for managing seat booking logic, waiting lists, and real-time availability with transaction error-handling.

3. Telecom Billing Systems: Telecom providers use PL/SQL to process millions of call records to calculate charges and generate bills for customers.

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Conclusion

For anyone dealing with databases, knowing the difference between SQL and PL/SQL is very important. SQL is best suited for simple operations such as returning or updating data, while PL/SQL is better for performing complex operations using programming logic. Learning both SQL and PL/SQL together will give you flexibility in dealing with actual database issues.

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