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Improve documentation of EXTRACT(WEEK).

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The docs showed that early-January dates can be considered part of the
previous year for week-counting purposes, but failed to say explicitly
that late-December dates can also be considered part of the next year.
Fix that, and add a cross-reference to the "isoyear" field.  Per bug
#7967 from Pawel Kobylak.
This commit is contained in:
Tom Lane 2013-03-18 13:34:15 -04:00
parent e016b72411
commit e39feb1006
1 changed files with 11 additions and 8 deletions
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19
doc/src/sgml/func.sgml
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@ -7151,16 +7151,19 @@ SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
<listitem>
<para>
The number of the week of the year that the day is in. By definition
(<acronym>ISO</acronym> 8601), the first week of a year
contains January 4 of that year. (The <acronym>ISO</acronym>-8601
week starts on Monday.) In other words, the first Thursday of
a year is in week 1 of that year.
(<acronym>ISO</acronym> 8601), weeks start on Mondays and the first
week of a year contains January 4 of that year. In other words, the
first Thursday of a year is in week 1 of that year.
</para>
<para>
Because of this, it is possible for early January dates to be part of the
52nd or 53rd week of the previous year. For example, <literal>2005-01-01</>
is part of the 53rd week of year 2004, and <literal>2006-01-01</> is part of
the 52nd week of year 2005.
In the ISO definition, it is possible for early-January dates to be
part of the 52nd or 53rd week of the previous year, and for
late-December dates to be part of the first week of the next year.
For example, <literal>2005-01-01</> is part of the 53rd week of year
2004, and <literal>2006-01-01</> is part of the 52nd week of year
2005, while <literal>2012-12-31</> is part of the first week of 2013.
It's recommended to use the <literal>isoyear</> field together with
<literal>week</> to get consistent results.
</para>
<screen>