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| author | Bruce Momjian <bruce@momjian.us> | 2018-06-23 23:32:41 -0400 |
|---|---|---|
| committer | Bruce Momjian <bruce@momjian.us> | 2018-06-23 23:32:41 -0400 |
| commit | c1975c1af7c2120277c57b1f40996b5d94cf22f6 (patch) | |
| tree | dc9514eb616a74e604d5795e143791fca06dfa54 | |
| parent | b742010890ab30dc0ef9e23fc341fc60d99b951a (diff) | |
| download | postgresql-c1975c1af7c2120277c57b1f40996b5d94cf22f6.tar.gz postgresql-c1975c1af7c2120277c57b1f40996b5d94cf22f6.zip | |
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
| -rw-r--r-- | doc/src/sgml/datatype.sgml | 40 |
1 files changed, 27 insertions, 13 deletions
diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml index 2284a48729b..2cfba1d36d2 100644 --- a/doc/src/sgml/datatype.sgml +++ b/doc/src/sgml/datatype.sgml @@ -2671,19 +2671,6 @@ P <optional> <replaceable>years</>-<replaceable>months</>-<replaceable>days</> < </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 <literal>'1.5 week'</> or <literal>'01:02:03.45'</>. Such input is @@ -2734,6 +2721,33 @@ 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"> |