Scott Bailey wrote:
Sam Mason wrote:
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!
This worked on both 8.3 and 8.4
SELECT *
FROM (
VALUES( '{}'::_xml),('{<root/>}'::_xml)
) sub
WHERE array_upper(column1, 1) > 0Sam Mason <sam@samason.me.uk>
And as Sam noted, array_upper needs to return null if the array is empty because 0 and -1 can be valid indexes for arrays in postgres.
Thanks, that's great, I'm delighted that there's a solution. Where exactly does that fit in terms of my original query, i.e.:
SELECT x
FROM (SELECT xpath('//entry[contains(p, ''searchtext'')]/@*', docxml)
AS x FROM docs) AS y WHERE x <> [test for empty array?????????]
-- Roy
