Re: Xpath Index in PostgreSQL

[Chris Roffler <croffler@xxxxxxxxxxxxx>]

Thanks for your fast response

I have the following sql statement now :

CREATE INDEX xml_index

  ON time_series

  USING btree

       (xpath('/AttributeList/Attributes/Attribute/Name/text()',external_attributes))[1]::text

And I am getting the following error :

ERROR:  syntax error at or near "["

LINE 6: ...butes/Attribute/Name/text()',external_attributes))[1]::text;

Any idea ?

Thanks 

Chris

                                                                                      ^

On Fri, Mar 5, 2010 at 3:22 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:

Chris Roffler <croffler@xxxxxxxxxxxxx> writes:
> I am trying to setup an index on an xpath _expression_ but the query never
> uses the index.
> Could someone enlighten me please ?

> Here is the setup :

> CREATE INDEX xml_index
>   ON time_series
>   USING btree
>   ((xpath('/AttributeList/Attributes/Attribute/Name/text()'::text,
> external_attributes)::text[]));

> And here is the query :

> select id, name
>  from
>   time_series
>  where
>  (xpath('/AttributeList/Attributes/Attribute/Name/text()',
> external_attributes))[1]::text='Attribute100'

Doesn't work that way --- subscripting isn't an indexable operation.
To make that query fast with a standard index, you'd need the index to
be on

       (xpath('/AttributeList/Attributes/Attribute/Name/text()',
       external_attributes))[1]::text

                       regards, tom lane