Re: BUG #8441: Recursive function in plpgsql does not seem to handle null values correctly

tvees@davincigroep.nl writes:
> CREATE OR REPLACE FUNCTION longlevenshtein (string1 character varying
> (1000000), string2 character varying (1000000)) RETURNS integer AS $$
>     BEGIN
>     IF  (length(coalesce($1, '')) = 0 AND length(coalesce($2, '')) = 0) THEN
>         RETURN 0;
>     ELSEIF ($1 IS NULL and $2 IS NOT NULL and length($2) > 0) THEN
>         RETURN length($2);
>     ELSEIF ($2 IS NULL and $1 IS NOT NULL and length($1)> 0) THEN
>         RETURN length($1);
>     ELSEIF length($1) = 0  AND length(coalesce($2, '')) > 0 THEN
>             RETURN length(coalesce($2, ''));
>         ELSEIF length($1) > 0 AND (length($2) = 0 or $2 is null) THEN
>             RETURN length(coalesce($1, ''));
>         ELSE
>         RETURN (Levenshtein(SUBSTRING($1 FROM 1 FOR 254), SUBSTRING($2 FROM 1
> for 254)) + longlevenshtein(coalesce(SUBSTRING($1 FROM 255), ''),
> coalesce(SUBSTRING($2 FROM 255), '')));
>     END IF;
>     END;
> $$ LANGUAGE plpgsql;

> When I invoke this function with
> SELECT longlevenshtein(null, 'foobar')
> I get a ERROR:  stack depth limit exceeded

Worksforme.  You sure you transcribed the function accurately?

Note however that sufficiently long input strings *will* drive this
function to stack overrun, if you don't run out of heap memory first
(I think the heap consumption will be O(N^2) ...).  Consider rewriting
it with a loop rather than recursion.

            regards, tom lane