Обсуждение: extracting from epoch values in pgsql
Hi folks,
I have a db that I need to draw some stats from. The db itself is from the
web application moodle which, perhaps to be cross-platform, uses unix epoch
times stored as integers throughout (see table description at end of mail).
I'd like to query some stats based on the appearance of objects over time,
ideally per month.
If the "time" were a pgsql timestamp, I'd probably do:
SELECT count(id), EXTRACT('month' FROM TIMESTAMP time) AS logmonth, EXTRACT('year' FROM TIMESTAMP time) AS
logyearFROMmdl_logWHERE action='login'GROUP BY logmonth,logyear;
but it's an epoch time, so I need to convert to a datestamp and then run
EXTRACT on that (as far as I can see. I can do the conversion easily
enough but I can't then pass that to extract(). I've tried:
SELECT EXTRACT('month',(TIMESTAMP WITH TIME ZONE 'epoch' + mdl_log.time * INTERVAL '1 second'))
FROM mdl_log;
SELECT time, to_timestamp(time) AS ts, EXTRACT('months',to_timestamp(time))
FROM mdl_log;
ERROR: syntax error at or near ","
LINE 1: ...t time, to_timestamp(time) AS ts, extract('months',to_times...
I also tried doing the extract on the alias "ts".
Am I doing something wrong here? Is this possible or do I need to approach
it in a different way? I've looked through the manual but I can't see a
way to convert epoch->timestamp and then use it further.
Thanks in advance,
Gavin
moodle-01-01-2009=# \d mdl_log Table "public.mdl_log"Column | Type |
Modifiers
--------+------------------------+------------------------------------------------------id | integer
|not null default nextval('mdl_log_id_seq'::regclass)time | integer | not null default 0userid |
integer | not null default 0ip | character varying(15) | not null default ''::character
varyingcourse| integer | not null default 0module | character varying(20) | not null default
''::charactervaryingcmid | integer | not null default 0url | character varying(100) | not null
default''::character varyinginfo | character varying(255) | not null default ''::character varyingaction | character
varying(40) | not null default ''::character varying
Indexes: "mdl_log_pkey" PRIMARY KEY, btree (id) "mdl_log_act_ix" btree (action) "mdl_log_cmi_ix" btree (cmid)
"mdl_log_coursemoduleaction_idx"btree (course, module, action) "mdl_log_tim_ix" btree ("time") "mdl_log_usecou_ix"
btree(userid, course)
Gavin McCullagh wrote:
> SELECT time, to_timestamp(time) AS ts, EXTRACT('months',to_timestamp(time))
> FROM mdl_log;
> ERROR: syntax error at or near ","
> LINE 1: ...t time, to_timestamp(time) AS ts, extract('months',to_times...
Try replacing extract('month',value) with extract('months' from value)
On Thu, 17 Sep 2009, Frank Bax wrote:
> Gavin McCullagh wrote:
>> SELECT time, to_timestamp(time) AS ts,
>> EXTRACT('months',to_timestamp(time)) FROM mdl_log;
>> ERROR: syntax error at or near ","
>> LINE 1: ...t time, to_timestamp(time) AS ts, extract('months',to_times...
>
> Try replacing extract('month',value) with extract('months' from value)
Makes no difference whether month or months:
moodle-01-01-2009=# select time, to_timestamp(time) AS ts, extract('month','to_timestamp(time)') from mdl_log LIMIT
10;
ERROR: syntax error at or near ","
LINE 1: ...ct time, to_timestamp(time) AS ts, extract('month','to_times...
^
moodle-01-01-2009=# select time, to_timestamp(time) AS ts, extract('months','to_timestamp(time)') from mdl_log LIMIT
10;
ERROR: syntax error at or near ","
LINE 1: ...t time, to_timestamp(time) AS ts, extract('months','to_times...
^
Gavin
2009/9/17 Gavin McCullagh <gavin.mccullagh@gcd.ie>:
> On Thu, 17 Sep 2009, Frank Bax wrote:
>
>> Gavin McCullagh wrote:
>>> SELECT time, to_timestamp(time) AS ts,
>>> EXTRACT('months',to_timestamp(time)) FROM mdl_log;
>>> ERROR: syntax error at or near ","
>>> LINE 1: ...t time, to_timestamp(time) AS ts, extract('months',to_times...
>>
>> Try replacing extract('month',value) with extract('months' from value)
>
> Makes no difference whether month or months:
>
> moodle-01-01-2009=# select time, to_timestamp(time) AS ts, extract('month','to_timestamp(time)') from mdl_log LIMIT
10;
> ERROR: syntax error at or near ","
> LINE 1: ...ct time, to_timestamp(time) AS ts, extract('month','to_times...
> ^
> moodle-01-01-2009=# select time, to_timestamp(time) AS ts, extract('months','to_timestamp(time)') from mdl_log LIMIT
10;
> ERROR: syntax error at or near ","
> LINE 1: ...t time, to_timestamp(time) AS ts, extract('months','to_times...
> ^
From manual:
http://www.postgresql.org/docs/current/interactive/functions-datetime.html
date_part('month',to_timestamp(time))
or
extract(month from to_timestamp(time))
Osvaldo
On Thu, 17 Sep 2009, Gavin McCullagh wrote:
> On Thu, 17 Sep 2009, Frank Bax wrote:
>
> > Gavin McCullagh wrote:
> >> SELECT time, to_timestamp(time) AS ts,
> >> EXTRACT('months',to_timestamp(time)) FROM mdl_log;
> >> ERROR: syntax error at or near ","
> >> LINE 1: ...t time, to_timestamp(time) AS ts, extract('months',to_times...
> >
> > Try replacing extract('month',value) with extract('months' from value)
>
> Makes no difference whether month or months:
Actually, I pasted a different query, but based on the one in my last
email:
moodle-01-01-2009=# SELECT EXTRACT('months',(TIMESTAMP WITH TIME ZONE 'epoch' + mdl_log.time * INTERVAL '1 second'))
FROM mdl_log;
ERROR: syntax error at or near ","
LINE 1: SELECT EXTRACT('months',(TIMESTAMP WITH TIME ZONE 'epoch' + ... ^
moodle-01-01-2009=# SELECT EXTRACT('month',(TIMESTAMP WITH TIME ZONE 'epoch' + mdl_log.time * INTERVAL '1 second'))
FROM mdl_log;
ERROR: syntax error at or near ","
LINE 1: SELECT EXTRACT('month',(TIMESTAMP WITH TIME ZONE 'epoch' + m... ^
Gavin
On Thu, 17 Sep 2009, Osvaldo Kussama wrote: > From manual: > http://www.postgresql.org/docs/current/interactive/functions-datetime.html > > date_part('month',to_timestamp(time)) > or > extract(month from to_timestamp(time)) Gah. I don't know I missed that. This works fine. SELECT extract(month from to_timestamp(time)) FROM mdl_log; Many thanks, Gavin
Gavin McCullagh wrote:
> On Thu, 17 Sep 2009, Frank Bax wrote:
>
>> Gavin McCullagh wrote:
>>> SELECT time, to_timestamp(time) AS ts,
>>> EXTRACT('months',to_timestamp(time)) FROM mdl_log;
>>> ERROR: syntax error at or near ","
>>> LINE 1: ...t time, to_timestamp(time) AS ts, extract('months',to_times...
>> Try replacing extract('month',value) with extract('months' from value)
>
> Makes no difference whether month or months:
Sorry; my typo. You used a comma in "extract" instead of "from".
On Thu, Sep 17, 2009 at 06:34:39PM +0100, Gavin McCullagh wrote:
> On Thu, 17 Sep 2009, Gavin McCullagh wrote:
>
> > On Thu, 17 Sep 2009, Frank Bax wrote:
> >
> > > Gavin McCullagh wrote:
> > >> SELECT time, to_timestamp(time) AS ts,
> > >> EXTRACT('months',to_timestamp(time)) FROM mdl_log;
> > >> ERROR: syntax error at or near ","
> > >> LINE 1: ...t time, to_timestamp(time) AS ts, extract('months',to_times...
> > >
> > > Try replacing extract('month',value) with extract('months' from value)
> >
> > Makes no difference whether month or months:
>
> Actually, I pasted a different query, but based on the one in my last
> email:
>
> moodle-01-01-2009=# SELECT EXTRACT('months',(TIMESTAMP WITH TIME ZONE 'epoch' + mdl_log.time * INTERVAL '1 second'))
> FROM mdl_log;
> ERROR: syntax error at or near ","
> LINE 1: SELECT EXTRACT('months',(TIMESTAMP WITH TIME ZONE 'epoch' + ...
> ^
> moodle-01-01-2009=# SELECT EXTRACT('month',(TIMESTAMP WITH TIME ZONE 'epoch' + mdl_log.time * INTERVAL '1 second'))
> FROM mdl_log;
> ERROR: syntax error at or near ","
> LINE 1: SELECT EXTRACT('month',(TIMESTAMP WITH TIME ZONE 'epoch' + m...
> ^
>
> Gavin
>
Gavin,
I think Frank had the answer:
Try replacing extract('month',value) with extract('months' from value)
Look at the documentation for the syntax for further details.
Regards,
Ken