Eddie Awad’s Blog - Latest Comments in Two Oracle PL/SQL Features You Probably Don’t Know About

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Steven Feuerstein — Wed, 25 Jun 2008 06:04:22 -0000

Wiz,

You can add subprograms to a package without losing other subprograms, but when you change a package and recompile, you lose package "state" - which means that the values of package level variables will no longer be valid and available in your session. No way to avoid this, except to reorganize your package into two separate packages: one that contains your subprograms and another that contains the variables.

Steven Feuerstein

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Wiz — Tue, 24 Jun 2008 06:31:44 -0000

hello,

I'm wondering if there is any way that someone could update and add a function to a package without loosing the other functions and or variables declared previously in that package

best regards,
Wiz

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Jeremy Bradshaw — Fri, 18 Jan 2008 07:10:06 -0000

The main reason you might not want to declare the mutually recursive procedures in the package specification, is that you might not want them visible from the outside, or you may only want one visible from the outside. Abstraction/information-hiding is a powerful concept.

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Siri — Sat, 24 Nov 2007 10:29:14 -0000

Just curious to know, how often one (have to) use 'mutual recursive functions' in a common work place?

~ Siri

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Eddie Awad — Tue, 15 May 2007 12:14:36 -0000

Ah! I see what you mean. Right, you have to "package" the two mutually recursive functions one way or another.

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Laurent Schneider — Tue, 15 May 2007 11:14:18 -0000

LOL ! There you have encapsulated two functions in one... it is almost a package!

Seriously, you cannot have

create function f1 return number is begin return f2; end;
/

create function f2 return number is begin return f1; end;
/

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Eddie Awad — Mon, 14 May 2007 16:04:42 -0000

Laurent, mutual recursion does not have to be coded in a package. The following stored function for example works like a charm:

  CREATE OR REPLACE FUNCTION odd_or_even (n NATURAL) 
     RETURN VARCHAR2
  IS
     l_return_var VARCHAR2 (4);

     FUNCTION odd (n NATURAL )
        RETURN BOOLEAN;   -- forward declaration

     FUNCTION even (n NATURAL)
        RETURN BOOLEAN
     IS
     BEGIN
        IF n = 0
        THEN
           RETURN TRUE;
        ELSE
           RETURN odd (n - 1);   -- mutually recursive call
        END IF;
     END even;

     FUNCTION odd (n NATURAL)
        RETURN BOOLEAN
     IS
     BEGIN
        IF n = 0
        THEN
           RETURN FALSE;
        ELSE
           RETURN even (n - 1);   -- mutually recursive call
        END IF;
     END odd;
  BEGIN
     IF even (n)
     THEN
        l_return_var := 'even';
     ELSIF odd (n)
     THEN
        l_return_var := 'odd';
     ELSE
        l_return_var := 'oops';
     END IF;

     RETURN l_return_var;
  END odd_or_even;
  /

Of course, as a general rule, I keep away from using standalone functions and procedures and use packages instead.

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Laurent Schneider — Sun, 13 May 2007 02:24:23 -0000

Do not you need a package to use mutual recursion?

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Eddie Awad — Thu, 03 May 2007 02:30:56 -0000

Don, yes you could, assuming that by package header you meant package specification, and assuming that your modules are created inside a package. In fact, that's one of the solutions I stated in my post: The second option is to declare my_func2 in the package specification.

However, what if you do not have a package? Instead you have CREATE FUNCTION for example.

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Don Seiler — Wed, 02 May 2007 17:43:07 -0000

Could you not put the declarations in the package header?

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Eddie Awad — Mon, 30 Apr 2007 12:43:40 -0000

Great analogy Laurent. Back in the old school days, I remember that the classic examples to demonstrate programming recursion were factorials and fibonacci numbers.

Re: Two Oracle PL/SQL Features You Probably Don’t Know About

Laurent Schneider — Mon, 30 Apr 2007 06:01:11 -0000

I had a good explanation of mutual recursion at school, a long time ago.

Simple recursion : you see yourself in a mirror, and in the mirror you see a small mirror where you see you again, and again.

Mutual recursion is : a boy is drawing a girl, the girl is drawing the boy (with a drawing of herself, drawing him, ...).

In Pascal, you had to add the keyword forward to do this.

Have a nice day,
Laurent