Re: xpath() subquery for empty array

On Sun, Jul 12, 2009 at 06:41:57PM +0100, Roy Walter wrote:
> Scott Bailey wrote:
> >Roy Walter wrote:
> >>How do I test for an empty array in postgres?
> >
> >WHERE x != array[]::xml[]
> >
> >
> Thanks Scott but that throws up a syntax error (at the closing bracket
> of array[]):
>
> ERROR: syntax error at or near "]"
> LINE 3: AS x FROM docs) AS y WHERE x != array[]::xml[]

Even if that syntax was correct it wouldn't work, xml values don't have
an equality operator defined for them. I've normally tested the array
size to figure out when they're empty, something like:

array_upper($1,1) > 0

However, I've just noticed that this returns NULL rather than zero as
I was expecting for an empty array (i.e. the literal '{}'). It also
doesn't seem to do useful things if you're using unusual bounds on your
array.

Bah, the semantics of arrays in PG always seem over-complicated to me!

--
Sam http://samason.me.uk/