How Do I Use Loops in PL/SQL for Data Processing

 Introduction

Loops in PL/SQL are essential for processing multiple rows of data or repeating a set of instructions until a condition is met. In Oracle APEX, using loops allows you to automate repetitive tasks such as updating records, performing calculations, or validating data efficiently. Understanding how to use different types of loops like FOR, WHILE, and simple LOOP structures helps you write clean, effective code for managing complex data processing scenarios.

In Oracle APEX, loops in PL/SQL help you process multiple rows of data or repeat tasks efficiently. Loops let you perform the same operation multiple times, such as updating records, validating data, or calculating values. There are three common types of loops in PL/SQL: simple LOOP, FOR LOOP, and WHILE LOOP. Each serves a different purpose depending on your processing needs.

Step 1: Using a Simple LOOP
A simple LOOP repeats indefinitely until you explicitly exit it with an EXIT statement. Use it when you don’t know the number of iterations in advance.

DECLARE
  v_counter NUMBER := 1;
BEGIN
  LOOP
    APEX_DEBUG.MESSAGE('Iteration: ' || v_counter);
    v_counter := v_counter + 1;
    EXIT WHEN v_counter > 5;
  END LOOP;
END;

Step 2: Using a FOR LOOP
FOR LOOP is useful when you know exactly how many times you want to repeat the code. It automatically handles the loop counter.

BEGIN
  FOR i IN 1..5 LOOP
    APEX_DEBUG.MESSAGE('Iteration: ' || i);
  END LOOP;
END;

Step 3: Using a WHILE LOOP
WHILE LOOP runs as long as a specified condition remains true. It checks the condition before each iteration.

DECLARE
  v_counter NUMBER := 1;
BEGIN
  WHILE v_counter <= 5 LOOP
    APEX_DEBUG.MESSAGE('Iteration: ' || v_counter);
    v_counter := v_counter + 1;
  END LOOP;
END;

Step 4: Looping Through Data with FOR LOOP and Cursor
You can use a FOR LOOP with an implicit cursor to process rows from a query.

BEGIN
  FOR rec IN (SELECT employee_id, first_name FROM employees WHERE department_id = 10) LOOP
    APEX_DEBUG.MESSAGE('Employee ID: ' || rec.employee_id || ', Name: ' || rec.first_name);
  END LOOP;
END;

Step 5: Best Practices

• Use FOR LOOPs when iterating over a known range or query result.

• Use EXIT WHEN inside simple LOOPs to control when the loop stops.

• Avoid infinite loops by ensuring your exit conditions are reachable.

• Use loops to minimize repetitive SQL calls and improve performance.

• Use APEX_DEBUG.MESSAGE or DBMS_OUTPUT.PUT_LINE for debugging your loop logic.

Using loops in PL/SQL within Oracle APEX helps automate repetitive tasks and process data efficiently. Understanding when and how to use each type of loop will improve your application's logic and performance.

Conclusion

Mastering loops in PL/SQL empowers you to handle bulk data operations and repetitive tasks smoothly within your Oracle APEX applications. By leveraging FOR, WHILE, and LOOP constructs, you can automate workflows, improve performance, and ensure consistent data handling. Using loops effectively is key to building scalable and maintainable applications that can process large amounts of data reliably.

Additional Example

Loops iterate over sets of data, making them useful for batch processing.

DECLARE

    v_emp_id EMPLOYEES.EMPLOYEE_ID%TYPE;

    v_salary EMPLOYEES.SALARY%TYPE;

BEGIN

    FOR rec IN (SELECT EMPLOYEE_ID, SALARY FROM EMPLOYEES) LOOP

        v_emp_id := rec.EMPLOYEE_ID;

        v_salary := rec.SALARY;

        IF v_salary < 50000 THEN

            UPDATE EMPLOYEES SET SALARY = SALARY * 1.10 WHERE EMPLOYEE_ID = v_emp_id;

        END IF;

    END LOOP;

END;

This loop increases the salary of employees earning less than 50,000 by 10%.