Oracle Pl/SQl: custom function with intermediate results

I need to transform a string into a number using some oracle built-in methods (parsing, strlength, ...)

I don't know how to assign a value to a variable inside the method, and I don't know where to put the declare section.

CREATE OR REPLACE FUNCTION EXAMPLE (param IN VARCHAR2) 
RETURN NUMBER AS
BEGIN

  SELECT <string_handling_using_param> 
    INTO var 
    FROM DUAL;

  RETURN TO_NUMBER(<some computation using var>);

END EXAMPLE ;

I have tried so开发者_Python百科me variation around this function, like adding an OUT parameter for storing the intermediate var, but then I can not call the function from regular SQL...

Any suggestion on how to achieve this ?

If I understand correctly you just need to define the "var" variable...

create or replace FUNCTION EXAMPLE (param IN VARCHAR2)
RETURN NUMBER
AS
   var VARCHAR2(100);  -- This datatype may need modification
BEGIN
  select <string_handling>
  into   var
  from   dual;

  return to_number(<some computation using var>);
END EXAMPLE ;

Depending on exactly what you're doing, there may be a better approach that doesn't need the SELECT ... FROM DUAL:

create or replace FUNCTION EXAMPLE (param IN VARCHAR2)
RETURN NUMBER
AS
   var VARCHAR2(100);  -- This datatype may need modification
BEGIN
  var := <string_handling>;

  return to_number(<some computation using var>);
END EXAMPLE ;

create or replace FUNCTION EXAMPLE (param IN VARCHAR2) 
RETURN NUMBER AS 
    -- declare section between AS and BEGIN
    var varchar2(100);
BEGIN   
   select <string_handling> into var from dual;  
   -- also note that many built-in functions can be done directly
   -- without calling a select, so in many cases
   -- var := substr(param,1,10) <or some other string handling>;
   -- is perfectly acceptable too. 
   return to_number(<some computation using var>); 
EXCEPTION -- if you need an exception handler
   when value_error then
      <do something with it or set a default return value or whatever>
END EXAMPLE ;