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Add two new format fields for use with to_char(), to_date() and

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to_timestamp():
    - ID for day-of-week
    - IDDD for day-of-year

This makes it possible to convert ISO week dates to and from text
fully represented in either week ('IYYY-IW-ID') or day-of-year
('IYYY-IDDD') format.

I have also added an 'isoyear' field for use with extract / date_part.

Brendan Jurd
This commit is contained in:
Bruce Momjian
2007-02-16 03:39:46 +00:00
parent c7b08050d9
commit 4ebb0cf9c3
12 changed files with 779 additions and 157 deletions
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58
doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.358 2007/02/14 18:46:08 petere Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.359 2007/02/16 03:39:44 momjian Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -4539,7 +4539,7 @@ SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
</row>
<row>
<entry><literal>I</literal></entry>
<entry>last digits of ISO year</entry>
<entry>last digit of ISO year</entry>
</row>
<row>
<entry><literal>BC</literal> or <literal>B.C.</literal> or
@ -4607,6 +4607,10 @@ SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
<entry><literal>DDD</literal></entry>
<entry>day of year (001-366)</entry>
</row>
<row>
<entry><literal>IDDD</literal></entry>
<entry>ISO day of year (001-371; day 1 of the year is Monday of the first ISO week.)</entry>
</row>
<row>
<entry><literal>DD</literal></entry>
<entry>day of month (01-31)</entry>
@ -4615,6 +4619,10 @@ SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
<entry><literal>D</literal></entry>
<entry>day of week (1-7; Sunday is 1)</entry>
</row>
<row>
<entry><literal>ID</literal></entry>
<entry>ISO day of week (1-7; Monday is 1)</entry>
</row>
<row>
<entry><literal>W</literal></entry>
<entry>week of month (1-5) (The first week starts on the first day of the month.)</entry>
@ -4625,7 +4633,7 @@ SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
</row>
<row>
<entry><literal>IW</literal></entry>
<entry>ISO week number of year (The first Thursday of the new year is in week 1.)</entry>
<entry>ISO week number of year (1 - 53; the first Thursday of the new year is in week 1.)</entry>
</row>
<row>
<entry><literal>CC</literal></entry>
@ -4791,6 +4799,27 @@ SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
</para>
</listitem>
<listitem>
<para>
An ISO week date (as distinct from a Gregorian date) can be specified to <function>to_timestamp</function> and <function>to_date</function> in one of two ways:
<itemizedlist>
<listitem>
<para>
Year, week and weekday, for example <literal>to_date('2006-42-4', 'IYYY-IW-ID')</literal> returns the date <literal>2006-10-19</literal>. If you omit the weekday it is assumed to be 1 (Monday).
</para>
</listitem>
<listitem>
<para>
Year and day of year, for example <literal>to_date('2006-291', 'IYYY-IDDD')</literal> also returns <literal>2006-10-19</literal>.
</para>
</listitem>
</itemizedlist>
</para>
<para>
Attempting to construct a date using a mixture of ISO week and Gregorian date fields is nonsensical, and could yield unexpected results. In the context of an ISO year, the concept of a 'month' or 'day of month' has no meaning. In the context of a Gregorian year, the ISO week has no meaning. Users should take care to keep Gregorian and ISO date specifications separate.
</para>
</listitem>
<listitem>
<para>
Millisecond (<literal>MS</literal>) and microsecond (<literal>US</literal>)
@ -5776,6 +5805,29 @@ SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40');
</listitem>
</varlistentry>
<varlistentry>
<term><literal>isoyear</literal></term>
<listitem>
<para>
The <acronym>ISO</acronym> 8601 year that the date falls in (not applicable to intervals).
</para>
<screen>
SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01');
<lineannotation>Result: </lineannotation><computeroutput>2005</computeroutput>
SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02');
<lineannotation>Result: </lineannotation><computeroutput>2006</computeroutput>
</screen>
<para>
Each <acronym>ISO</acronym> year begins with the Monday of the week containing the 4th of January, so in early January or late December the <acronym>ISO</acronym> year may be different from the Gregorian year. See the <literal>week</literal> field for more information.
</para>
<para>
This field is not available in PostgreSQL releases prior to 8.3.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>microseconds</literal></term>
<listitem>