Re: Adding xpath_exists function

On Thu, May 6, 2010 at 5:53 PM, <mike(at)mlfowler(dot)com> wrote:
> Quoting Robert Haas <robertmhaas(at)gmail(dot)com>:
>
>>
>> I'm not sure I understand how this more convenient than just using
>> xpath() with exists()?
>>
>
> It will save a lot of complexity in WHERE clauses. For example using
> exists() in xpath() you might construct something like:
>
> WHERE array_dims(xpath('exists(/foo/bar)','<bar><foo/></bar>'::xml) IS NOT
> NULL ...
>
> Whereas a dedicated xpath_exists() would look like:
>
> WHERE xpath_exists('/foo/bar','<bar><foo/></bar>'::xml) ....
>
> I accept this example is quite basic, but I hope it illustrates the added
> usability. I think xml in sql is complex enough, especially when you start
> considering namespaces, that anything we can do to simplify common use cases
> can only help improve the uptake of postgres xml.

Oh, I see. Well, that might be reasonable syntactic sugar, although I
think you should make it wrap the path in exists() unconditionally,
rather than testing for an existing wrap.

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--
Robert Haas
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