Re: syntax for reaching into records, specifically ts_stat results

On Tue, 9 Dec 2008, Dan Chak wrote:

> Oleg,
>
> This syntax works fine until I also want to get the "sentence_id" column in
> there as well, so that I can differentiate one set of ts_stat results from
> another. With the syntax where ts_stat is treated like a table, it isn't
> possible to run ts_stat separately on multiple tsvectors as I'm doing below.
>
> Is there some generic record access syntax that I can use?

write function

>
> Thanks,
> Dan
>
> On Dec 9, 2008, at 3:04 PM, Oleg Bartunov wrote:
>
>> try select * from ts_stat(....)
>> btw, performance of ts_stat() was greatly improved in 8.4.
>>
>> Oleg
>> On Tue, 9 Dec 2008, Dan Chak wrote:
>>
>>> Dear Postgres Folk,
>>>
>>> In working with tsvectors (added in 8.3), I've come to a place where my
>>> syntax-fu has failed me. I've resorted to turning a result set of records
>>> into strings so that I can regexp out the record fields I need, rather
>>> than access them directly, as I'm sure it's possible to do with the right
>>> syntactic formulation. Although my solution works, I'm sure it's much
>>> less efficient than it could be, and hope someone on the list can help do
>>> this the right way.
>>>
>>> Basically, I would like to transpose a series of tsvectors (one per row)
>>> into columns. E.g., as tsvects, I have this:
>>>
>>> test=# select * from tsvects;
>>> sentence_id | tsvect
>>> -------------+------------------------------
>>> 1 | 'fox':3 'brown':2 'quick':1
>>> 2 | 'lazi':1 'eleph':3 'green':2
>>>
>>> Instead I want this:
>>>
>>> sentence_id | word | freq
>>> -------------+-------+------
>>> 1 | fox | 1
>>> 1 | brown | 1
>>> 1 | quick | 1
>>> 2 | lazi | 1
>>> 2 | eleph | 1
>>> 2 | green | 1
>>>
>>> I am able to generate this with the following view, but the problem is
>>> that to create it, I must first cast the ts_stat results to a string, and
>>> then regexp out the pertinent pieces:
>>>
>>> create or replace view words as
>>> select sentence_id,
>>> substring(stat from '^\\(([^,]+),') as word,
>>> substring(stat from ',([^,]+)\\)$') as freq
>>> from (select sentence_id,
>>> ts_stat('select tsvect from tsvects where sentence_id = ' ||
>>> tsvects.sentence_id)::text as stat
>>> from tsvects
>>> ) as foo;
>>>
>>> It seems like there should be a way to access fields in the records
>>> returned from ts_stat directly, but I can't figure out how. Here's the
>>> result of the subquery:
>>>
>>> test=# select sentence_id,
>>> ts_stat('select tsvect from tsvects where sentence_id = ' ||
>>> tsvects.sentence_id)::text as stat
>>> from tsvects;
>>> sentence_id | stat
>>> -------------+-------------
>>> 1 | (fox,1,1)
>>> 1 | (brown,1,1)
>>> 1 | (quick,1,1)
>>> 2 | (lazi,1,1)
>>> 2 | (eleph,1,1)
>>> 2 | (green,1,1)
>>> (6 rows)
>>>
>>> If I try to get at the elements (which I believe are named 'word', 'ndoc',
>>> 'nentry'), I get a variety of syntax errors:
>>>
>>> test=# select sentence_id,
>>> test-# stat['word'],
>>> test-# stat['nentry']
>>> test-# from (select sentence_id,
>>> test(# ts_stat('select tsvect from tsvects where
>>> sentence_id = ' ||
>>> test(# tsvects.sentence_id) as stat
>>> test(# from tsvects
>>> test(# ) as foo;
>>> ERROR: cannot subscript type record because it is not an array
>>>
>>> If I say stat.word (instead of subscripting), I get 'missing FROM-clause
>>> entry for table "stat"'. If I say foo.stat.word, I get 'ERROR: schema
>>> "foo" does not exist'.
>>>
>>> Any ideas on how to get into these records with resorting to text parsing?
>>>
>>> Thanks,
>>> Dan
>>>
>>>
>>
>> Regards,
>> Oleg
>> _____________________________________________________________
>> Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
>> Sternberg Astronomical Institute, Moscow University, Russia
>> Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
>> phone: +007(495)939-16-83, +007(495)939-23-83
>
>
>

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83