[HACKERS] syntax for reaching into records, specifically ts_stat results
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
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Re: [HACKERS] syntax for reaching into records, specifically ts_stat results
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?
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: [EMAIL PROTECTED], http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83
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Re: [HACKERS] syntax for reaching into records, specifically ts_stat results
That works perfectly! Thanks, Dan On Dec 9, 2008, at 3:13 PM, Tom Lane wrote: Dan Chak [EMAIL PROTECTED] writes: 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'. I think the syntax you need is (stat).word etc. See Field Selection here: http://www.postgresql.org/docs/8.3/static/sql-expressions.html#AEN1679 The reason for the parens is exactly to distinguish whether the leading word is a table or column name. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
