Understanding PL/SQL in Oracle APEX

PL/SQL (Procedural Language/Structured Query Language) is Oracle’s procedural extension of SQL, and it plays a critical role in Oracle APEX development. In Oracle APEX, PL/SQL is used to define business logic, control data processing, interact with the database, and automate workflows within applications. Understanding PL/SQL is essential for building powerful, data-driven applications that go beyond basic form and report functionality.

PL/SQL is essential in APEX because it allows you to:

• Implement business logic within an application

• Create dynamic actions and processes

• Perform validations and error handling

• Write stored procedures and functions

• Manage triggers and packages for better modularity

Where PL/SQL is Used in Oracle APEX

• Page Processes: PL/SQL is commonly used in page processes to perform actions such as inserting, updating, or deleting data after a form is submitted.

• Validations: You can write PL/SQL logic to validate user input before saving it to the database.

• Dynamic Actions: When a page element triggers a dynamic action, PL/SQL can be used on the server side to execute logic and return results to the client.

• Application Processes: For actions that apply across multiple pages or during session initialization, PL/SQL is written in application-level processes.

• PL/SQL Regions: These allow developers to embed PL/SQL directly in a page to generate custom HTML output or perform logic-driven display.

PL/SQL Code Structure
PL/SQL code is typically written in the form of anonymous blocks or stored procedures and follows this structure:

DECLARE
  -- variable declarations
BEGIN
  -- executable statements
EXCEPTION
  -- error handling
END;

What Are the Differences Between SQL and PL/SQL Code Structure

SQL and PL/SQL are both used in Oracle APEX and Oracle Database, but they have different code structures and purposes. Understanding the difference helps you use each correctly in your applications.
1. SQL Code Structure
SQL is a declarative language.
It works with one statement at a time.
Each SQL command performs a specific task like retrieving or modifying data.
SQL does not support control structures like IF or LOOP.
Example of SQL code structure:
SELECT first_name, last_name FROM employees WHERE department_id = 10;

Other SQL examples:
INSERT INTO departments (department_name) VALUES ('Marketing');
UPDATE employees SET salary = 5000 WHERE employee_id = 101;
DELETE FROM employees WHERE employee_id = 102;

2. PL/SQL Code Structure
PL/SQL is a procedural language that includes SQL and additional programming features.
It allows multiple statements in a block.
It supports variables, loops, conditions, and error handling.
PL/SQL is used to build stored procedures, functions, and anonymous blocks.

Basic PL/SQL block structure:
DECLARE
  v_name VARCHAR2(50);
BEGIN
  SELECT first_name INTO v_name FROM employees WHERE employee_id = 101;
  DBMS_OUTPUT.PUT_LINE('Employee Name: ' || v_name);
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    DBMS_OUTPUT.PUT_LINE('No employee found.');
END;

Key differences in structure:
SQL has no DECLARE, BEGIN, or EXCEPTION sections.
PL/SQL uses a block structure: DECLARE (optional), BEGIN, EXCEPTION (optional), and END.
SQL is for querying or updating data. PL/SQL is for building logic and control.
Summary
Use SQL when you need a single query or data manipulation command.
Use PL/SQL when you need to write logic that includes multiple steps, variables, or error handling.

Both are essential in Oracle APEX development and often work together to build dynamic, data-driven applications.

Common Use Cases in APEX

• Automatically updating audit fields (created date, modified by)

• Performing complex validations based on multiple inputs

• Sending emails or notifications using APEX_MAIL

• Inserting or updating multiple related tables in one process

• Calling stored procedures and packages for backend operations

Benefits of Using PL/SQL in APEX

• Performance: Code runs inside the database, reducing network overhead.

• Reusability: Logic written once in procedures or functions can be reused across different pages or applications.

• Security: Business rules are enforced at the database level, reducing reliance on UI-based validation.

• Maintainability: Keeps complex logic out of the page and centralized in packages or procedures.

SQL (Structured Query Language) and PL/SQL (Procedural Language/SQL) are both used in Oracle databases, but they serve different purposes and have different capabilities. Here's a clear breakdown:

1. Purpose

• SQL is a declarative language used to interact with the database — for querying, inserting, updating, and deleting data.

• PL/SQL is a procedural language that extends SQL with programming features like loops, conditions, variables, and error handling.

2. Execution

• SQL executes one statement at a time (single-line operations).

• PL/SQL can execute multiple statements as a block, including logic and control flow.

3. Language Type

• SQL is a data manipulation language (DML).

• PL/SQL is a procedural language that embeds SQL statements inside structured code.

4. Capabilities

• SQL can:

  • Select data (SELECT)

  • Insert, update, delete records

  • Create and modify database objects

• PL/SQL can:

  • Declare variables and constants

  • Use loops (FOR, WHILE) and conditions (IF, CASE)

  • Handle exceptions (EXCEPTION block)

  • Define procedures, functions, packages, and triggers

5. Reusability

• SQL is typically written and run per use case.

• PL/SQL allows you to create reusable blocks like stored procedures and functions.

6. Performance

• PL/SQL improves performance by reducing round-trips between application and database, especially in complex logic.

• SQL may require multiple calls to achieve the same, especially in procedural logic.

7. Example

SQL Example:

SELECT first_name FROM employees WHERE department_id = 10;

PL/SQL Example:

DECLARE
  v_name employees.first_name%TYPE;
BEGIN
  SELECT first_name INTO v_name FROM employees WHERE employee_id = 101;
  DBMS_OUTPUT.PUT_LINE('Name: ' || v_name);
END;

Summary

• Use SQL when you need to interact with data directly (query or modify).

• Use PL/SQL when you need to perform logic, automation, or control flow inside the database.
  Both are often used together in Oracle APEX and database development to build powerful, efficient applications

When to Use PL/SQL vs. SQL

SQL is used when you need to perform simple operations directly on the data, such as selecting, inserting, updating, or deleting rows in a table. It is best for straightforward queries and data manipulation tasks. Use SQL when you want to retrieve data from a table, filter it with conditions, or make basic changes to one or more records.

PL/SQL should be used when you need to include logic, decision-making, or processing that involves more than one SQL statement. It is ideal when your task requires conditions, loops, error handling, or variables. PL/SQL is useful for writing stored procedures, functions, packages, and triggers where the operations are more complex or need to be reused across different parts of the application.

Use SQL for single operations on data. Use PL/SQL when you need to wrap SQL in a logical structure that includes control flow, calculations, or exception handling. In Oracle APEX, PL/SQL is often used in page processes, validations, and backend logic, while SQL is used for queries, report sources, and data display.

Where Do We Use PL/SQL and SQL in Oracle APEX

In Oracle APEX, both PL/SQL and SQL are used throughout the application to manage data and implement business logic. SQL is used for querying and manipulating data, while PL/SQL is used when procedural logic, conditions, or loops are needed. They often work together to power the dynamic behavior of APEX applications.

Where SQL is Used

• In report regions to fetch data using SELECT statements

• In form regions to read and write table data

• In LOVs (List of Values) to populate dropdowns with query results

• In validations and computations to retrieve or calculate values

• In dynamic actions that execute SQL statements to get results quickly

Where PL/SQL is Used

• In page processes to insert, update, delete, or validate data with logic

• In page-level or application-level validations using conditional rules

• In page-level or region-level dynamic PL/SQL code blocks

• In PL/SQL anonymous blocks for executing stored procedures or functions

• In before and after submit processes to control page flow or behavior

• In custom authentication, authorization, and session management logic

SQL is best used when you are interacting with the data directly. PL/SQL is used when you need to wrap those interactions with logic, conditions, or exception handling. Oracle APEX makes it easy to combine both, so you can create responsive, intelligent, and secure applications.

Where Inside Oracle APEX Do We Add PL/SQL and SQL Code

Oracle APEX provides several areas where you can directly add PL/SQL and SQL code to control how your application behaves and interacts with the database. These areas are built into the APEX Page Designer and SQL Workshop, making it easy to use SQL for data access and PL/SQL for procedural logic.

1. SQL Workshop

• Use SQL Commands to write and run ad hoc SQL and PL/SQL.

• Use SQL Scripts to save and execute longer SQL or PL/SQL blocks.

• Use Object Browser to create tables, views, procedures, and functions using SQL and PL/SQL.

2. Report and Form Regions

• In Classic or Interactive Reports, you use SQL queries to define the data source.

• In Forms, SQL is used to fetch and save data directly from tables or views.

• You can also use PL/SQL for logic-based column values using expressions or functions.

3. Page Processes

• PL/SQL is added here to run after page submission or on page load.

• Used for inserting, updating, or deleting records with custom logic.

• Useful for calling stored procedures or performing validations.

4. Dynamic Actions

• PL/SQL can be added as server-side code when a dynamic action is triggered.

• SQL can be used as part of true/false condition checks or value assignments.

5. Computations

• Add SQL or PL/SQL code to calculate or set page item values before or after page rendering.

6. Validations

• PL/SQL expressions or functions are used to create custom validation rules for form items.

• SQL queries can be used to check if a value exists or meets specific conditions.

7. LOVs (List of Values)

• SQL queries are used to populate dropdowns, radio groups, and checkbox groups with dynamic values from the database.

8. Page Items and Regions

• You can set default values using SQL queries.

• PL/SQL expressions can be used in conditions to show or hide items or regions.

9. Application Processes and Shared Components

• PL/SQL can be defined as a global process or function to be reused across pages.

• Useful for authentication, authorization, and session-level operations.

10. PL/SQL Dynamic Content Regions

• Allows you to write full PL/SQL blocks that generate HTML output directly within a region.

Oracle APEX is tightly integrated with SQL and PL/SQL, allowing you to apply database logic exactly where it’s needed — whether it’s displaying data, validating inputs, or controlling behavior at the page or application level.

Conclusion
PL/SQL is the backbone of dynamic and powerful Oracle APEX applications. It allows developers to implement complex logic, enforce business rules, and interact efficiently with the database. By mastering PL/SQL, you gain full control over your application's behavior, making it more robust, secure, and scalable. Whether you're processing data, validating input, or building custom logic, PL/SQL is an essential tool in your APEX toolkit.