PL/SQL vs SQL

Programming languages form the backbone of data-driven society and, nowadays, play a critical role in handling, analysing, or processing data. Among all this use, SQL and PL/SQL are t

he most widely used languages currently in use. These forms of the language can be termed as belonging to the ecosystem of Oracle-they appear similar but are different, designed for different purposes, serving different needs, and used for different applications. It will discuss the differences between SQL and PL/SQL, uniquely explore such capabilities of both, PL/SQL Features, SQL vs PL/SQL Performance, Differences between SQL and PL/SQL and list benefits of PL/SQL over the standard SQL. In summary, the performances as between these two will be detailedly explicated by a comparative analysis.

Introduction to SQL and PL/SQL

Before looking at how SQL and PL/SQL differ, let’s first know what SQL and PL/SQL are.

• SQL (Structured Query Language): SQL is a standard language for accessing and manipulating databases. It is used to retrieve, update, delete, and insert data into databases. SQL is declarative, meaning you specify what you want to do with the data, and the database engine takes care of the rest.
• PL/SQL (Procedural Language/SQL): PL/SQL is Oracle’s procedural extension of SQL. While SQL can execute a single query at a time, PL/SQL allows for procedural programming, which means you can write code with logic (loops, conditions, variables) to perform more complex operations in a batch. PL/SQL integrates seamlessly with SQL, giving developers more control over database operations.

Key Differences Between SQL and PL/SQL

To help you understand the differences between SQL and PL/SQL, the following table summarizes the key aspects of each:

Criteria	SQL	PL/SQL
Nature	Declarative language	Procedural language
Purpose	Used for data manipulation	Used for writing complex programs with logic
Execution	Executes a single query at a time	Executes a block of code, including multiple queries
Error Handling	Limited error handling	Supports robust error handling using exceptions
Control Structures	No control structures (loops, conditions)	Supports loops, conditions, and branches
Performance	Single query execution	Can batch SQL statements, reducing overhead
Reusability	Queries cannot be reused directly	Can reuse procedures and functions
Interaction	Direct interaction with the database	Requires SQL for database interaction

Features of SQL

SQL is the fundamental language used for accessing databases and is meant to query and manipulate data. Its most fundamental facilities are:

• Data Retrieval: SQL gives you the facility of retrieving data from the database using the SELECT statement, very frequently accompanied by filtering, sorting, or aggregation functions like WHERE, ORDER BY, or GROUP BY.
• Data Manipulation: SQL also supports data manipulation with the INSERT, UPDATE, and DELETE statements.
• Data Definition: Besides defining data, SQL also allows a person to define and control the database structure through create, alter, and drop statements.
• Transaction Control: SQL allows both COMMIT and ROLLBACK TRANSACTION CONTROL commands to ensure integrity of data.

Example of SQL in Action

Here is a basic SQL query that retrieves employee names and salaries from an “employees” table:

SELECT employee_name, salary
FROM employees
WHERE department = 'IT'
ORDER BY salary DESC;

This query selects the names and salaries of all employees in the IT department and orders the results by salary in descending order.

Features of PL/SQL:

PL/SQL extends the capabilities of SQL by allowing developers to write full programs that include control structures, variables, error handling, and more. The key PL/SQL features are:

• Block Structure: PL/SQL organizes code into blocks with three sections. The declaration section defines variables, the execution section contains SQL and logic, and the exception section handles errors.
• Control Structures: PL/SQL supports procedural logic like loops (FOR, WHILE), conditions (IF-THEN-ELSE), and branches (CASE).
• Error Handling: PL/SQL offers strong error-handling capabilities using EXCEPTION blocks to handle unexpected errors while executing the application.
• Procedures and Functions: You can develop reusable blocks of code in the form of procedures (which execute actions) and functions (which return a value).

Example of PL/SQL Block

Here’s an example of a simple PL/SQL block that calculates the total salary for all employees in a department:

DECLARE
  total_salary NUMBER;
BEGIN
  SELECT SUM(salary) INTO total_salary FROM employees WHERE department_id = 101;
  DBMS_OUTPUT.PUT_LINE('Total salary for department 101 is ' || total_salary);
END;

This block retrieves the total salary for a specific department and prints the result.

SQL vs PL/SQL Performance

The interesting point is that PL/SQL and SQL have their very distinct strengths in performance. SQL is designed to allow for fast querying of data bases making it appropriate for applications where speedy retrieval of data is the need. However, when complex logic and multiple queries are required, SQL becomes inefficient. This is where PL/SQL comes in.

Performance Comparison Table

Aspect	SQL Performance	PL/SQL Performance
Query Execution	Executes individual queries efficiently	Efficient for executing batches of queries
Network Traffic	High network traffic for multiple queries	Reduces network traffic by bundling multiple queries
Complex Logic	Not suitable for handling complex logic	Can handle complex logic with control structures
Error Handling	Limited error handling, can slow down operations	Robust error handling minimizes downtime

SQL vs PL/SQL in Batch Processing

Imagine you have a requirement to update the salaries of all employees in a department. Using SQL alone, you would need to execute multiple UPDATE statements for each employee, leading to increased network traffic and slower performance. In PL/SQL, you can perform these updates in a single block, reducing overhead and improving efficiency.

For example:

• SQL Example:

UPDATE employees
SET salary = salary * 1.10
WHERE department_id = 101;

• PL/SQL Example:

BEGIN
  FOR emp IN (SELECT employee_id FROM employees WHERE department_id = 101) LOOP
    UPDATE employees SET salary = salary * 1.10 WHERE employee_id = emp.employee_id;
  END LOOP;
END;

In PL/SQL, you can perform multiple updates within a loop. This minimizes interaction between the application and the database server, enhancing overall performance.

Benefits of PL/SQL

PL/SQL offers several advantages over SQL, making it a preferred choice for many Oracle developers. Some of the key benefits of PL/SQL include:

• Increased Flexibility: PL/SQL supports procedural programming, which allows for the creation of complex logic and control structures. This flexibility is particularly useful in scenarios that require more than just simple data manipulation.
• Code Reusability: With PL/SQL, you can write reusable code in the form of procedures and functions, which can be called multiple times in different parts of the application.
• Reduced Network Traffic: PL/SQL allows multiple SQL statements to be bundled into a single block, reducing the number of interactions between the application and the database. This reduces network overhead and speeds up execution.
• Robust Error Handling: PL/SQL’s built-in error-handling capabilities make it easier to build robust applications that can recover from unexpected issues without crashing.

Benefits Comparison Table

Benefits	SQL	PL/SQL
Error Handling	Basic error handling	Advanced error handling through exceptions
Logic Handling	No procedural logic	Supports procedural logic, loops, and conditions
Reusability	Queries cannot be reused directly	Supports reusable procedures and functions
Performance in Batch Jobs	Suitable for simple queries	Better for batch processing and multiple statements
Network Traffic	Higher network traffic for multiple queries	Reduces network traffic with bundled queries

Real World Use Cases

Now, let’s have some look at real-world examples where SQL and PL/SQL are used together for different purposes.

Example: Retrieving Data with SQL

One report generation tool may have to pull out information from the database for creating a report. SQL should be used in such queries because it supports fast retrieval. For example:

SELECT customer_id, customer_name, total_purchases
FROM customers
WHERE region = 'North America'
ORDER BY total_purchases DESC;

Example: Complex Business Logic with PL/SQL

However, when business logic involves conditional rules and multiple queries, PL/SQL offers significant advantages. For example, discounts can be applied based on total purchases.

BEGIN
  FOR rec IN (SELECT customer_id, total_purchases FROM customers WHERE region = 'North America') LOOP
    IF rec.total_purchases > 10000 THEN
      UPDATE customers
      SET discount = 0.10
      WHERE customer_id = rec.customer_id;
    ELSE
      UPDATE customers
      SET discount = 0.05
      WHERE customer_id = rec.customer_id;
    END IF;
  END LOOP;
END;

PL/SQL efficiently handles complex logic for updating customer discounts. This is based on their purchase history, all within a single block of code.