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| author | Bruce Momjian <bruce@momjian.us> | 2018-06-23 23:32:42 -0400 |
|---|---|---|
| committer | Bruce Momjian <bruce@momjian.us> | 2018-06-23 23:32:42 -0400 |
| commit | b6e94b820a21146b898232bc3e3920b31198e637 (patch) | |
| tree | 9141026b7d41ee8e40012ece2b66ab09fe6e341a | |
| parent | 2d502b81289f679a8244a0b6c94a4d294968bde1 (diff) | |
| download | postgresql-b6e94b820a21146b898232bc3e3920b31198e637.tar.gz postgresql-b6e94b820a21146b898232bc3e3920b31198e637.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 67bae322878..cc54cc8a583 100644 --- a/doc/src/sgml/datatype.sgml +++ b/doc/src/sgml/datatype.sgml @@ -2671,19 +2671,6 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>- </para> <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. Functions - <function>justify_days</function> and <function>justify_hours</function> 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'</literal> or <literal>'01:02:03.45'</literal>. Such input is @@ -2734,6 +2721,33 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>- </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"> |