Functions and procedures in packages can be overloaded. The following package TEST has two procedures called print_number, which behave differently depending on parameters they are called with.

create or replace package TEST is
  procedure print_number(p_number in integer);
  procedure print_number(p_number in varchar2);
end TEST;
/
create or replace package body TEST is

  procedure print_number(p_number in integer) is
  begin
    dbms_output.put_line('Digit: ' || p_number);    
  end;
  
  procedure print_number(p_number in varchar2) is
  begin
    dbms_output.put_line('String: ' || p_number);    
  end;

end TEST;
/

We call both procedures. The first with integer parameter, the second with varchar2.

set serveroutput on;
-- call the first procedure
exec test.print_number(3);
-- call the second procedure
exec test.print_number('three');

The output of the above script is:

SQL> 
Digit: 3
PL/SQL procedure successfully completed
String: three
PL/SQL procedure successfully completed

Restrictions on Overloading

Only local or packaged subprograms, or type methods, can be overloaded. Therefore, you cannot overload standalone subprograms. Also, you cannot overload two subprograms if their formal parameters differ only in name or parameter mode

In this example we define a package header and a package body wit a function.
After that we are calling a function from the package that return a return value.

Package header:

CREATE OR REPLACE PACKAGE SkyPkg AS

       FUNCTION GetSkyColour(vPlanet IN VARCHAR2)
       RETURN VARCHAR2;
       
END;
/

Package body:

CREATE OR REPLACE PACKAGE BODY SkyPkg AS

        FUNCTION GetSkyColour(vPlanet IN VARCHAR2)
        RETURN VARCHAR2
        AS
               vColour VARCHAR2(100) := NULL;
        BEGIN
               IF vPlanet = 'Earth' THEN
                       vColour := 'Blue';
               ELSIF vPlanet = 'Mars' THEN
                       vColour := 'Red';
               END IF;

               RETURN vColour;
        END;
        
END;
/

Calling the function from the package body:

DECLARE
        vColour VARCHAR2(100);
BEGIN
        vColour := SkyPkg.GetSkyColour(vPlanet => 'Earth');
        DBMS_OUTPUT.PUT_LINE(vColour);
END;
/

Packages in PLSQL are a collection of procedures, functions, variables, exceptions, constants, and data structures. Generally the resources in a package are related to each other and accomplish similar tasks.

Why Use Packages

• Modularity
• Better Performance/ Funtionality

Parts of a Package

Specification - Sometimes called a package header. Contains variable and type declarations and the signatures of the functions and procedures that are in the package which are public to be called from outside the package.

Package Body - Contains the code and private declarations.

The package specification must be compiled before the package body, otherwise the package body compilation will report an error.

Syntax