8000 Clarify input/output timezone information. · postgrespro/postgres_cluster@f8a9892 · GitHub
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Thomas G. Lockhart
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Clarify input/output timezone information.
Add detail on exact interpretation of "concatenated date" for various lengths.
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‎doc/src/sgml/datetime.sgml

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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/datetime.sgml,v 2.3 1999/05/26 17:30:28 thomas Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/datetime.sgml,v 2.4 1999/06/23 06:17:51 thomas Exp $
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Date/time details
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$Log: datetime.sgml,v $
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Revision 2.4 1999/06/23 06:17:51 thomas
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Clarify input/output timezone information.
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Add detail on exact interpretation of "concatenated date"
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for various lengths.
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Revision 2.3 1999/05/26 17:30:28 thomas
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Add chapters on CVS access, MVCC, SQL theory to the docs.
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Add an appendix with more details on date/time attributes and handling.
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<title>Time Zones</title>
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<para>
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<productname>Postgres</productname> must have internal tabular
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information for time zone decoding, since there is no *nix standard
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system interface to provide access to general, cross-timezone
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information. The underlying OS <emphasis>is</emphasis> used to
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provide time zone information for <emphasis>output</emphasis>.
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<table tocentry="1">
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<title><productname>Postgres</productname> Recognized Time Zones</title>
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<titleabbrev>Time Zones</titleabbrev>
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<step>
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<para>
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The token is a number or number field.
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If there are more than 4 digits,
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and if no other date fields have been previously read, then interpret
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as a "concatenated date" (e.g. <literal>19990118</literal>).
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</para>
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<substeps>
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<step>
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<para>
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If there are more than 4 digits,
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and if no other date fields have been previously read, then interpret
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as a "concatenated date" (e.g. <literal>19990118</literal>).
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as a "concatenated date" (e.g. <literal>19990118</literal>). 8
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and 6 digits are interpreted as year, month, and day, while 7
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and 5 digits are interpreted as year, day of year.
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</para>
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</step>
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<step>
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<para>
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If three digits and a year has already been decoded, then interpret as day of year.
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If the token is three digits
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and a year has already been decoded, then interpret as day of year.
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</para>
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</step>
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<step>
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<para>
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If BC has been specified, negate the year and offset by one
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(there is no year zero in the Gregorian calendar).
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If BC has been specified, negate the year and offset by one for
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internal storage
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(there is no year zero in the Gregorian calendar, so numerically
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1BC becomes year zero).
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</para>
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</step>
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If BC was not specified, and if the year field was two digits in length, then
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adjust the year to 4 digits. If the field was less than 70, then add 2000;
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otherwise, add 1900.
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<tip>
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<para>
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Gregorian years 1-99AD may be entered by using 4 digits with leading
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zeros (e.g. 0099 is 99AD). Three digits are also accepted as a
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year under most circumstances, though depending on position the
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numeric string may
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be interpreted as doy instead.
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</para>
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</tip>
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</para>
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</step>
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</procedure>
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</sect1>
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</note>
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<para>
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The Julian Day invented by the French scholar
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The Julian Day was invented by the French scholar
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Joseph Justus Scaliger (1540-1609)
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and which probably takes its name from the Scaliger's father,
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and probably takes its name from the Scaliger's father,
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the Italian scholar Julius Caesar Scaliger (1484-1558).
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Astronomers have used the Julian period to assign a unique number to
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every day since 1 January 4713 BC. This is the so-called Julian Day
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</para>
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<para>
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Julian Day is different from Julian Date.
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<quote>Julian Day</quote> is different from <quote>Julian Date</quote>.
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The Julian calendar was introduced by Julius Caesar in 45 BC. It was
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in common use until the 1582, when countries started changing to the
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<simplelist>
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<member>
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Every year divisible by 4 is a leap year.
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Every year divisible by 4 is a leap year.
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</member>
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<member>
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However, every year divisible by 100 is not a leap year.
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However, every year divisible by 100 is not a leap year.
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</member>
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<member>
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However, every year divisible by 400 is a leap year after all.
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However, every year divisible by 400 is a leap year after all.
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</member>
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</simplelist>
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