From: Khangelani Gama <kgama@argility.com>
References: <203fb35202e040e00d0d3ed514414a2a@mail.gmail.com>
 <1422336077879-5835589.post@n5.nabble.com>
In-Reply-To: <1422336077879-5835589.post@n5.nabble.com>
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Date: Tue, 27 Jan 2015 07:25:19 +0200
Message-ID: <7f2e8f98693a575fcebb1376116b27de@mail.gmail.com>
Subject: Re: Postgres 9.2 - XML string functions ?
To: David G Johnston <david.g.johnston@gmail.com>, pgsql-admin@postgresql.org
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Sender: pgsql-admin-owner@postgresql.org

Thank you very much

-----Original Message-----
From: pgsql-admin-owner@postgresql.org
[mailto:pgsql-admin-owner@postgresql.org] On Behalf Of David G Johnston
Sent: 27 January 2015 07:21 AM
To: pgsql-admin@postgresql.org
Subject: Re: [ADMIN] Postgres 9.2 - XML string functions ?

Khangelani Gama-2 wrote
> Hi
>
>
>
> Please help, I have been asked why XML string functions do this, which
> is why does the second statement below return no rows. No matter what
> is on the select statement, they can select as many columns as they
> want but the XML function breaks it as soon as it is added.
>
>
>
>
>
> 1)      select
> aud_id,act_typ,right(act_typ::text,1),fpp_cde,obo_aud_id,obo_aud_id||s
> ku_cde as "Key" from sku_tran join audit using (aud_id) join
> action_typ using
> (act_typ) join branch using (br_cde) join sku using (sku_cde) where
> obo_aud_id=5252005 and audit.fpp_cde between '201408' and '201412' and
> (right(act_typ::text,1) = '5') and act_typ between 76000 and 76999;
>
> aud_id  | act_typ | right | fpp_cde | obo_aud_id |       Key
>
> 2585912 |   76005 | 5     | 201408  |    5252005 | 525200510053486
>
> (1 row)
>
> 2)      select
> aud_id,act_typ,right(act_typ::text,1),fpp_cde,obo_aud_id,(unnest(xpath
> ('.//checksumBr/text()', aud_xml::xml)))::text||obo_aud_id||sku_cde as
> "Key" from sku_tran join audit using (aud_id) join action_typ using
> (act_typ) join branch using
> (br_cde) join sku using (sku_cde) where obo_aud_id=5252005 and
> audit.fpp_cde between '201408' and '201412' and
> (right(act_typ::text,1) =
> '5') and act_typ between 76000 and 76999;
>
> aud_id | act_typ | right | fpp_cde | obo_aud_id | Key
>
> (0 rows)

When you unnest an empty array it returns an empty set.  An empty set in
the select list causes the row it is sourced from to be excluded from the
output.

You can use a correlated subselect to instead have the result instead be
shown as NULL.

David J.


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