Thread: (Fwd) Hi and some advice on Dates
G'day All, I am pretty new to postgres and am using it as a backend for DB's accessed via the web and Perl DBI. All this works really well and I have a few db's up and running on our Intranet at work, where they're quite heavily used. My current project requires me to do some date calculations and I'm stumped ! Could anyone help with the following: (I have not fixed data type yet, I will be guided by any info I can get) How to query a table and look for any records where the value in a date field is greater than (say) 10 days ago Calculate the difference between two times on the same day. (I have experimented with age() and it sort of does wht I want..is there any other way ?) I've searched the archives without success and the doc's don't give much away as far as this type of thing goes. Thanks in anticipation. Andrew -------------------------------------------------------- Andrew Mather: System Administrator, VIAS mathera@woody.agvic.gov.au / amsm@deakin.edu.au http://www.deakin.edu.au/~amsm/index.html Ph: 03 92174342 (BH), Mob 0413 009 761 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Linux: it's not just for breakfast anymore. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-
Andrew Mather <mathera@woody.agvic.gov.au> wrote:
> How to query a table and look for any records where the value in a
> date field is greater than (say) 10 days ago
Maybe like this:
-- create a(n example) table:
=> create table xxx (d date, something text);
CREATE
=> insert into xxx values ('09.11.1998', 'bbbbb!');
INSERT 72800 1
=> insert into xxx values ('02.11.1998', 'aaaa!');
INSERT 72801 1
=> insert into xxx values ('08.11.1998', 'cccc!');
INSERT 72802 1
-- have a look (note that I'm using the 'German' date style)
=> select * from xxx;
d|something
----------+---------
09.11.1998|bbbbb!
02.11.1998|aaaa!
08.11.1998|cccc!
(3 rows)
'today' gives current date when casted ('::' operator) to 'date' type;
the calculation of difference is simple:
=> select * from xxx
where d between 'today'::date - 10 and 'today'::date;
d|something
----------+---------
02.11.1998|aaaa!
08.11.1998|cccc!
(2 rows)
> Calculate the difference between two times on the same day. (I have
> experimented with age() and it sort of does wht I want..is there any
> other way ?)
There are various possibilities, depends on what you want. For
calculating another 'datetime', try:
=> select 'now'::datetime as now,
'now'::datetime - '10 secs'::timespan as ten_s_ago;
now |ten_s_ago
--------------------------+--------------------------
08.11.1998 09:59:54.00 MET|08.11.1998 09:59:44.00 MET
(1 row)
You have to cast to a proper type; e.g., you can't do
WRONG! => select 'now'::time as now,
WRONG! 'now'::time - '10 secs'::timespan as ten_s_ago;
probably because the 'time'-type doesn't know anything about the fact
that midnight is the beginning of a new day and everything is set to
zero ...
For calculating a 'timespan', do
=> select 'now'::datetime - '08.11.1998 06:00'::datetime as interv;
interv
------------------------
@ 4 hours 6 mins 30 secs(1 row)
or
=> select date_part('epoch',
'now'::datetime - '08.11.1998 06:00'::datetime)
as interv;
interv
-------
7708135
(1 row)
if you need the result in seconds.
Hope it helps!
Ulf
--
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Andrew Mather wrote: > Could anyone help with the following: (I have not fixed data type yet, > I will be guided by any info I can get) > > How to query a table and look for any records where > the value in a date field is greater than (say) 10 days ago > > Calculate the difference between two times on the same day. (I have > experimented with age() and it sort of does wht I want..is there any > other way ?) Use Perl as a database interface and have a look at de Perl module Date::Manip. It has all you need, and more. -- Best regards, Wybo ===================Servalys Analytical Chemistry Services================= Wybo H. Dekker | Deilsedijk 60 | tel +31-345-652164 wybo@servaly.hobby.nl | 4158 CH Deil, The Netherlands | fax +31-345-652383
G'day , Thanks for your reply. > > How to query a table and look for any records where > > the value in a date field is greater than (say) 10 days ago > > > > Calculate the difference between two times on the same day. (I have > > experimented with age() and it sort of does wht I want..is there any > > other way ?) > > Use Perl as a database interface and have a look at de Perl module > Date::Manip. It has all you need, and more. > Will have a look ! I am using perl for an interface to this db anyway. I didn't realise there was a date module ! Andrew -------------------------------------------------------- Andrew Mather: System Administrator, VIAS mathera@woody.agvic.gov.au / amsm@deakin.edu.au http://www.deakin.edu.au/~amsm/index.html Ph: 03 92174342 (BH), Mob 0413 009 761 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- NEWS! Police begin campaign to run down jaywalkers -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-