From e8616362da3419f81c802a665315c7b411eae2f4 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Sat, 23 Jun 2018 23:32:41 -0400
Subject: [PATCH] doc: show how interval's 3 unit buckets behave using
EXTRACT()
This clarifies when justify_days() and justify_hours() are useful.
Paragraph moved too.
Reported-by: vodevsh@gmail.com
Discussion: https://postgr.es/m/152698651482.26744.15456677499485530703@wrigleys.postgresql.org
Backpatch-through: 9.3
---
doc/src/sgml/datatype.sgml | 40 +++++++++++++++++++++++++-------------
1 file changed, 27 insertions(+), 13 deletions(-)
diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index 8bbbd88fcc3..071b9bc1dce 100644
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -2661,19 +2661,6 @@ P <optional> <replaceable>years</>-<replaceable>months</>-<replaceable>days</> <
to each field if any field is negative.
</para>
- <para>
- Internally <type>interval</> values are stored as months, days,
- and seconds. This is done because the number of days in a month
- varies, and a day can have 23 or 25 hours if a daylight savings
- time adjustment is involved. The months and days fields are integers
- while the seconds field can store fractions. Because intervals are
- usually created from constant strings or <type>timestamp</> subtraction,
- this storage method works well in most cases. Functions
- <function>justify_days</> and <function>justify_hours</> are
- available for adjusting days and hours that overflow their normal
- ranges.
- </para>
-
<para>
In the verbose input format, and in some fields of the more compact
input formats, field values can have fractional parts; for example
@@ -2725,6 +2712,33 @@ P <optional> <replaceable>years</>-<replaceable>months</>-<replaceable>days</> <
</tgroup>
</table>
+ <para>
+ Internally <type>interval</type> values are stored as months, days,
+ and seconds. This is done because the number of days in a month
+ varies, and a day can have 23 or 25 hours if a daylight savings
+ time adjustment is involved. The months and days fields are integers
+ while the seconds field can store fractions. Because intervals are
+ usually created from constant strings or <type>timestamp</type> subtraction,
+ this storage method works well in most cases, but can cause unexpected
+ results:
+
+<programlisting>
+SELECT EXTRACT(hours from '80 minutes'::interval);
+ date_part
+-----------
+ 1
+
+SELECT EXTRACT(days from '80 hours'::interval);
+ date_part
+-----------
+ 0
+</programlisting>
+
+ Functions <function>justify_days</function> and
+ <function>justify_hours</function> are available for adjusting days
+ and hours that overflow their normal ranges.
+ </para>
+
</sect2>
<sect2 id="datatype-interval-output">
--
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