Re: [GENERAL] string_to_array with empty input

[Greg Stark <greg(dot)stark(at)enterprisedb(dot)com>]

Sorry for top-posting--blame apple.

Hm my first instinct was indeed to make it a zero-length array. I was  
thinking of the input as a "list" and surely there are no elements in  
a list which empty. I had to think a while until a length-1 array made  
sense.

I suppose the thinking was string_to_array is the inverse of an  
array_to_string operation then there are multiple possible answers.  
You might have joined a zero length or a singleton array of an empty  
string....
and since it's unknown which was the original value null is the right  
answer...

I agree that picking an arbitrary choice is going to be more useful in  
practice though.

--
Greg


On 30 Mar 2009, at 23:26, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Steve Crawford <scrawford(at)pinpointresearch(dot)com> writes:
> > I have a query that converts a string to an array with the
> > string_to_array function. Sometimes the input is an empty string  
> > (not a
> > null, but a string of zero-length). I had expected the result to be a
> > one-element array with an empty string as the first and only  
> > element but
> > instead it returned null. I looked at the docs and didn't find the
> > observed behavior documented.
>
> The behavior is pretty intentional according to the source code:
>
>    /* return NULL for empty input string */
>    if (inputstring_len < 1)
>    {
>        text_position_cleanup(&state);
>        PG_RETURN_NULL();
>    }
>
> I agree this seems less than consistent though, especially seeing
> that you *don't* get a null for a zero-length separator, which if
> anything is a more poorly defined case.
>
> I doubt it'd be a good idea to back-patch a change for this,
> but I could see altering the definition for 8.4.
>
> Does anyone want to argue for keeping it the same?  Or perhaps
> argue that a zero-element array is a more sensible result than
> a one-element array with one empty string?  (It doesn't seem
> like it to me, but maybe somebody thinks so.)
>
>            regards, tom lane
>
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