From: Bruce Momjian <bruce@momjian.us>
To: Daniel Grace <dgrace@wingsnw.com>
Cc: pgsql-docs@postgresql.org
Subject: Re: Missing documentation for uses of extract(field from interval)
Date: Fri, 11 Mar 2011 08:18:29 -0500 (EST)
Message-ID: <201103111318.p2BDITc09295@momjian.us> (raw)
In-Reply-To: <AANLkTinq_cgsuqgjkM5-R+anvSxTLdG6CD45nsVWCHG4@mail.gmail.com>
I have added documentation for EXTRACT(DAY) usage with intervals. We
had something for MONTH, but for some reason nothing for DAY. Applied
patch attached.
---------------------------------------------------------------------------
Daniel Grace wrote:
> (Note: I'm not subscribed to pgsql-docs, so please CC me on any
> replies. Thanks!)
>
> I pulled up the documentation today to see if I could get just the
> number of days in an interval using EXTRACT. The answer provided was
> vague: While you can use EXTRACT(field from interval) (shown in table
> 9-27), section 9.9.1 only lists:
>
> day
>
> The day (of the month) field (1 - 31)
>
> SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
> Result: 16
>
>
>
> It turns out that EXTRACT(day FROM interval) does work as expected --
> so perhaps the documentation should be updated to something like:
>
> day
>
> The day (of the month) field (1 - 31), or the number of days in the interval
>
> SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
> Result: 16
>
> SELECT EXTRACT(DAY FROM INTERVAL '42 days 21:00:00');
> Result: 42
>
> Likewise for month, year, century and maybe some others. (hour,
> minute, and *second{s?} probably don't need updated text).
>
> There also should probably be some warning in here about EXTRACT on
> intervals however. Namely cases like this:
>
> SELECT EXTRACT(YEAR FROM INTERVAL '400 days') --> Result: 0
> (because the interval is '400 days' not '1 year 35 days')
> SELECT EXTRACT(DAY FROM INTERVAL '1 year') --> Result: 0 (because
> the interval is '1 year' not '365 days')
> SELECT EXTRACT(DAY FROM INTERVAL '1 month') --> Result: 0
>
> Though, this works:
> SELECT EXTRACT(CENTURY FROM INTERVAL '99 years') --> Result: 0
> SELECT EXTRACT(CENTURY FROM INTERVAL '100 years') --> Result: 1
> --
> Daniel Grace
> AGE, LLC
> System Administrator and Software Developer
>
> --
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--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
Attachments:/rtmp/interval.diff (text/x-diff, 1.8K) downloaddiff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgmlnew file mode 100644index 4635cf2..c392109
*** a/doc/src/sgml/func.sgml
--- b/doc/src/sgml/func.sgml
*************** SELECT EXTRACT(CENTURY FROM TIMESTAMP '2
*** 6605,6617 ****
<term><literal>day</literal></term>
<listitem>
<para>
! The day (of the month) field (1 - 31)
</para>
<screen>
SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>16</computeroutput>
</screen>
</listitem>
</varlistentry>
--- 6605,6624 ----
<term><literal>day</literal></term>
<listitem>
<para>
! For <type>timestamp</type> values, the day (of the month) field
! (1 - 31) ; for <type>interval</type> values, the number of days
</para>
<screen>
SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>16</computeroutput>
+ + SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute');+ <lineannotation>Result: </lineannotation><computeroutput>40</computeroutput>
</screen>
+ + +
</listitem>
</varlistentry>
*************** SELECT EXTRACT(MINUTE FROM TIMESTAMP '20
*** 6827,6833 ****
<listitem>
<para>
For <type>timestamp</type> values, the number of the month
! within the year (1 - 12) ; for <type>interval</type> values
the number of months, modulo 12 (0 - 11)
</para>
--- 6834,6840 ----
<listitem>
<para>
For <type>timestamp</type> values, the number of the month
! within the year (1 - 12) ; for <type>interval</type> values,
the number of months, modulo 12 (0 - 11)
</para>
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To: pgsql-docs@postgresql.org
Cc: bruce@momjian.us, dgrace@wingsnw.com
Subject: Re: Missing documentation for uses of extract(field from interval)
In-Reply-To: <201103111318.p2BDITc09295@momjian.us>
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