PL/SQL For Practitioners – #6 Functions

Hi folks,

A user-defined function is a set of PL/SQL statements you can call by name. Functions are very similar to procedures, except that a function returns a value to the environment in which it is called.

Syntax

CREATE OR REPLACE
FUNCTION <name> (<paramete1_name parameter1_type, .. ,parametern_name parametern_type>) RETURN <return type> 
AS
  --local variables(optional)
BEGIN
  --your code
END <name>;

Example 1

The following example is a function responsible to return the next available city id from the table city. It is a simple algorithm, but enough to demonstrate the usage of this feature.

You can use the following script to create and populate this table. create_and_populate_tables_city_and_country

Function

CREATE OR REPLACE
FUNCTION F_GET_NEW_CITY_ID RETURN NUMBER AS
   v_new_id number := 0;
   v_is_an_used_id varchar2(1) := 'N';
BEGIN
  
  select max(nvl(id, 0)) + 1 into v_new_id from city;
  
  LOOP
  
    BEGIN
      select 'Y' into v_is_an_used_id from city where id = v_new_id;
    EXCEPTION
      WHEN NO_DATA_FOUND THEN
        v_is_an_used_id := 'N';
    END;
    
    EXIT WHEN v_is_an_used_id = 'N';
    
    v_new_id := v_new_id +1;
    
  END LOOP;
  
  RETURN v_new_id;
  
END F_GET_NEW_CITY_ID;

How to test/execute in an anonymous block

No matter where you are executing or calling a function, you always must use a declared variable to receive the return from this function.

DECLARE
  v_Return NUMBER;
BEGIN

  v_Return := F_GET_NEW_CITY_ID;
  DBMS_OUTPUT.PUT_LINE('v_Return = ' || v_Return);
  
END;

Result

Example 2

Function

create or replace
FUNCTION F_CHECK_CITY_NAME (p_city_name IN VARCHAR2) RETURN BOOLEAN AS
   v_is_an_used_id varchar2(1) := 'N';
BEGIN
  
  SELECT NVL('Y', 'N') INTO v_is_an_used_id FROM CITY WHERE UPPER(name) = UPPER(p_city_name);
  
  IF v_is_an_used_id = 'Y' THEN
    RETURN TRUE;
  ELSE
    RETURN FALSE;
  END IF;
  
END F_CHECK_CITY_NAME;

How to test/execute in an anonymous block

DECLARE
  P_CITY_NAME VARCHAR2(200);
  v_Return BOOLEAN;
BEGIN
  P_CITY_NAME := 'CURITIBA';

  v_Return := F_CHECK_CITY_NAME(
    P_CITY_NAME => P_CITY_NAME
  );
  IF (v_Return) THEN 
    DBMS_OUTPUT.PUT_LINE('v_Return = ' || 'TRUE');
  ELSE
    DBMS_OUTPUT.PUT_LINE('v_Return = ' || 'FALSE');
  END IF;
END;

Result

This post is part of a series about the most common structures in PL/SQL. You can check the rest of them in the link below.

PL/SQL for real world – 8 features that you have to know

Please write down in the comments any further questions you may have. I’ll be happy to help you.

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