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Doc: add info about timestamps with fractional-minute UTC offsets.
Our code has supported fractional-minute UTC offsets for ages, but there was no mention of the possibility in the main docs, and only a very indirect reference in Appendix B. Improve that. Discussion: https://postgr.es/m/162543102827.697.5755498651217979813@wrigleys.postgresql.org
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‎doc/src/sgml/datatype.sgml

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@@ -1977,19 +1977,27 @@ MINUTE TO SECOND
19771977
</row>
19781978
<row>
19791979
<entry><literal>04:05:06.789-8</literal></entry>
1980-
<entry>ISO 8601</entry>
1980+
<entry>ISO 8601, with time zone as UTC offset</entry>
19811981
</row>
19821982
<row>
19831983
<entry><literal>04:05:06-08:00</literal></entry>
1984-
<entry>ISO 8601</entry>
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<entry>ISO 8601, with time zone as UTC offset</entry>
19851985
</row>
19861986
<row>
19871987
<entry><literal>04:05-08:00</literal></entry>
1988-
<entry>ISO 8601</entry>
1988+
<entry>ISO 8601, with time zone as UTC offset</entry>
19891989
</row>
19901990
<row>
19911991
<entry><literal>040506-08</literal></entry>
1992-
<entry>ISO 8601</entry>
1992+
<entry>ISO 8601, with time zone as UTC offset</entry>
1993+
</row>
1994+
<row>
1995+
<entry><literal>040506+0730</literal></entry>
1996+
<entry>ISO 8601, with fractional-hour time zone as UTC offset</entry>
1997+
</row>
1998+
<row>
1999+
<entry><literal>040506+07:30:00</literal></entry>
2000+
<entry>UTC offset specified to seconds (not allowed in ISO 8601)</entry>
19932001
</row>
19942002
<row>
19952003
<entry><literal>04:05:06 PST</literal></entry>
@@ -2025,25 +2033,29 @@ MINUTE TO SECOND
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<entry><literal>PST8PDT</literal></entry>
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<entry>POSIX-style time zone specification</entry>
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</row>
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<row>
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<entry><literal>-8:00:00</literal></entry>
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<entry>UTC offset for PST</entry>
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</row>
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<row>
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<entry><literal>-8:00</literal></entry>
2030-
<entry>ISO-8601 offset for PST</entry>
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<entry>UTC offset for PST (ISO 8601 extended format)</entry>
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</row>
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<row>
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<entry><literal>-800</literal></entry>
2034-
<entry>ISO-8601 offset for PST</entry>
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<entry>UTC offset for PST (ISO 8601 basic format)</entry>
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</row>
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<row>
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<entry><literal>-8</literal></entry>
2038-
<entry>ISO-8601 offset for PST</entry>
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<entry>UTC offset for PST (ISO 8601 basic format)</entry>
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</row>
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<row>
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<entry><literal>zulu</literal></entry>
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<entry>Military abbreviation for UTC</entry>
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</row>
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<row>
20452057
<entry><literal>z</literal></entry>
2046-
<entry>Short form of <literal>zulu</literal></entry>
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<entry>Short form of <literal>zulu</literal> (also in ISO 8601)</entry>
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</row>
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</tbody>
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</tgroup>
@@ -2393,6 +2405,24 @@ TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+02'
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</tgroup>
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</table>
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<para>
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In the <acronym>ISO</acronym> style, the time zone is always shown as
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a signed numeric offset from UTC, with positive sign used for zones
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east of Greenwich. The offset will be shown
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as <replaceable>hh</replaceable> (hours only) if it is an integral
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number of hours, else
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as <replaceable>hh</replaceable>:<replaceable>mm</replaceable> if it
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is an integral number of minutes, else as
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<replaceable>hh</replaceable>:<replaceable>mm</replaceable>:<replaceable>ss</replaceable>.
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(The third case is not possible with any modern time zone standard,
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but it can appear when working with timestamps that predate the
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adoption of standardized time zones.)
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In the other date styles, the time zone is shown as an alphabetic
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abbreviation if one is in common use in the current zone. Otherwise
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it appears as a signed numeric offset in ISO 8601 basic format
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(<replaceable>hh</replaceable> or <replaceable>hhmm</replaceable>).
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</para>
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<para>
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The date/time style can be selected by the user using the
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<command>SET datestyle</command> command, the <xref

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