Обсуждение: Recusrive Functions in 7.0.3

Are recursive functions allowed in in 7.0.3 as I seem to be unable to get them to work in plpgsql, it just freezes and
Ihave to do ctrl-alt-c.
 
ie calling the same function name from within some form of loop, possible to 4 or 5 levels?

Also is it possible to output any debugging info, all I really want to be able to do is print out a variable to the
screen.

Final quesion for pure speed on functions does PL/PGSQL have special compilation options or would I get better
performacefor PL/C?
 

Regards

Mark

<plpgsql@polar-digital.com> writes:
> Are recursive functions allowed in in 7.0.3

Sure.

play=> create function myfactorial(int) returns int as '
play'> begin
play'>   if $1 > 1 then
play'>     return $1 * myfactorial($1 - 1);
play'>   end if;
play'>   return $1;
play'> end;' language 'plpgsql';
CREATE
play=> select myfactorial(1);myfactorial
-------------          1
(1 row)

play=> select myfactorial(10);myfactorial
-------------    3628800
(1 row)

play=>

I get a stack overflow crash at about myfactorial(7500), but that seems
like a sufficient level of recursion depth for normal purposes ...

> as I seem to be unable to
> get them to work in plpgsql,

Are you sure you aren't asking for infinite recursion, eg by invoking
the same function with the same argument?
        regards, tom lane

mark proctor <m.proctor@bigfoot.com> writes:
> However if I put the PERFORM line back in to create a recursive
> function it just goes on forever, and I only have 6 nodes. 

Hm.  There may be a bug here, or maybe you're still confused... but I'm
not eager to reverse-engineer your table declarations and data from this
sketch.  Would you mind providing a complete example, ie a SQL script to
reproduce the problem starting from an empty database?
        regards, tom lane

Ahh I found what I was doing wrong, there was a rogue value being returned causing to infinite loop. Its fixed now. 
Creating that script you recommended set my thinking process straight.

many thanks

Mark

On Saturday 10 February 2001 08:42, Tom Lane wrote:
> mark proctor <m.proctor@bigfoot.com> writes:
> > However if I put the PERFORM line back in to create a recursive
> > function it just goes on forever, and I only have 6 nodes.
>
> Hm.  There may be a bug here, or maybe you're still confused... but I'm
> not eager to reverse-engineer your table declarations and data from this
> sketch.  Would you mind providing a complete example, ie a SQL script to
> reproduce the problem starting from an empty database?
>
>             regards, tom lane

If I remove the line calling PERFORM it works without problems moving the children node for the passed integer into
testand then exiting.
 
I can then repeat the process going through the output to test iteratively and do not have any problems.
However if I put the PERFORM line back in to create a recursive function it just goes on forever, and I only have 6
nodes.

CREATE FUNCTION get_children (integer) RETURNS integer AS
'   DECLARE       pnode_parent ALIAS FOR $1;       rec RECORD;   BEGIN       FOR rec IN SELECT * FROM
tree_adjacency_matrixWHERE node_parent = pnode_parent LOOP               INSERT INTO test (node1, node2)
VALUES(rec.node_child,rec.node_parent);               PERFORM get_children(rec.node_child);       END LOOP;
RETURN0;   END;
 
'LANGUAGE 'plpgsql'  

Mark


On Saturday 10 February 2001 03:29, Tom Lane wrote:
> <plpgsql@polar-digital.com> writes:
> > Are recursive functions allowed in in 7.0.3
>
> Sure.
>
> play=> create function myfactorial(int) returns int as '
> play'> begin
> play'>   if $1 > 1 then
> play'>     return $1 * myfactorial($1 - 1);
> play'>   end if;
> play'>   return $1;
> play'> end;' language 'plpgsql';
> CREATE
> play=> select myfactorial(1);
>  myfactorial
> -------------
>            1
> (1 row)
>
> play=> select myfactorial(10);
>  myfactorial
> -------------
>      3628800
> (1 row)
>
> play=>
>
> I get a stack overflow crash at about myfactorial(7500), but that seems
> like a sufficient level of recursion depth for normal purposes ...
>
> > as I seem to be unable to
> > get them to work in plpgsql,
>
> Are you sure you aren't asking for infinite recursion, eg by invoking
> the same function with the same argument?
>
>             regards, tom lane