Working with Arrays in Oracle PL/SQL

In Oracle PL/SQL, arrays are a fundamental data structure that can be used to store and manipulate collections of data. In this tutorial, we will explore how to create and work with arrays in PL/SQL.

Introduction to Arrays

An array is a collection of elements of the same data type stored in contiguous memory locations. In PL/SQL, you can create an array using one of several built-in types: VARRAY, TABLE, or associative arrays (also known as index-by tables).

Creating a VARRAY

A VARRAY is a fixed-size array that can be used to store a collection of elements. To create a VARRAY, you need to specify the type and size of the array.

DECLARE
   TYPE array_t IS VARRAY(3) OF VARCHAR2(10);
   array array_t := array_t('Matt', 'Joanne', 'Robert');
BEGIN
   FOR i IN 1..array.COUNT LOOP
       DBMS_OUTPUT.PUT_LINE(array(i));
   END LOOP;
END;

Creating a TABLE

A TABLE is an unbounded array that can be used to store a collection of elements. To create a TABLE, you need to specify the type of the array.

DECLARE
   TYPE array_t IS TABLE OF VARCHAR2(10);
   array array_t := array_t();
BEGIN
   FOR i IN 1..3 LOOP
      array.EXTEND(); -- Extend the array
      array(i) := 'x';
   END LOOP;
   
   FOR i IN 1..array.COUNT LOOP
       DBMS_OUTPUT.PUT_LINE(array(i));
   END LOOP;
END;

Creating an Associative Array

An associative array is a collection of elements that can be accessed by their index. To create an associative array, you need to specify the type and index of the array.

DECLARE
   TYPE employee_arraytype IS TABLE OF VARCHAR2(10) INDEX BY PLS_INTEGER;
   employee_array employee_arraytype;
BEGIN
   employee_array(1) := 'Matt';
   employee_array(2) := 'Joanne';
   employee_array(3) := 'Robert';
   
   FOR i IN 1..employee_array.COUNT LOOP
       DBMS_OUTPUT.PUT_LINE(employee_array(i));
   END LOOP;
END;

Creating an Oracle-Defined Collection

Oracle provides several predefined collection types, such as SYS.ODCIVARCHAR2LIST, that can be used to create arrays.

DECLARE 
  arrayvalues sys.odcivarchar2list;
BEGIN
  arrayvalues := sys.odcivarchar2list('Matt','Joanne','Robert');
  FOR x IN ( SELECT m.column_value m_value
               FROM TABLE(arrayvalues) m )
  LOOP
    DBMS_OUTPUT.PUT_LINE (x.m_value||' is a good pal');
  END LOOP;
END;

Best Practices

When working with arrays in PL/SQL, it’s essential to follow best practices:

• Use the correct data type for your array elements.
• Initialize and extend your array as needed.
• Use loops to iterate over your array elements.
• Avoid using arrays that are too large, as they can consume a lot of memory.

By following these guidelines and examples, you can effectively work with arrays in Oracle PL/SQL and improve the performance and efficiency of your code.