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Clarify age() 'months' calculation documentation.

This commit is contained in:
Bruce Momjian 2007-09-14 00:52:45 +00:00
parent f307fe4c9b
commit dfe2e3f7a5
1 changed files with 8 additions and 9 deletions
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17
doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.392 2007/08/31 21:33:48 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.393 2007/09/14 00:52:45 momjian Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -5906,14 +5906,13 @@ SELECT (DATE '2001-02-16', INTERVAL '100 days') OVERLAPS
</para>
<para>
Note that when the <function>age</> function operates on multi-month
intervals, <productname>PostgreSQL</> adds days to the earlier date
until full months can be added. This yields a different result than
adding full months first if the interval crosses from one month to the
next. For example, <literal>age('2004-06-01', '2004-04-30')</> yeilds
<literal>1 mon 1 day</> using the <productname>PostgreSQL</> method,
while adding the month first would yield <literal>1 mon 2 days</>
because May has 31 days, while April has only 30.
Note there can be ambiguity in the <literal>months</> returned by
<function>age</> because different months have a different number of
days. <productname>PostgreSQL</>'s approach uses the month from the
earlier of the two dates when calculating partial months. For example,
<literal>age('2004-06-01', '2004-04-30')</> uses April to yield
<literal>1 mon 1 day</>, while using May would yield <literal>1 mon 2
days</> because May has 31 days, while April has only 30.
</para>
<sect2 id="functions-datetime-extract">