datetime.sgml

关系型数据库 Postgresql 6.5.2

      <row>
       <entry>ADT</entry>
       <entry>-03:00 </entry>
       <entry>Atlantic Daylight Time</entry>
      </row>
      <row>
       <entry>NFT</entry>
       <entry>-3:30</entry>
       <entry>Newfoundland Standard Time</entry>
      </row>
      <row>
       <entry>NST</entry>
       <entry>-3:30</entry>
       <entry>Newfoundland Standard Time</entry>
      </row>
      <row>
       <entry>AST</entry>
       <entry>-4:00 </entry>
       <entry>Atlantic Std Time (Canada)</entry>
      </row>
      <row>
       <entry>EDT</entry>
       <entry>-4:00 </entry>
       <entry>Eastern Daylight Time</entry>
      </row>
      <row>
       <entry>ZP4</entry>
       <entry>-4:00</entry>
       <entry>GMT +4 hours</entry>
      </row>
      <row>
       <entry>CDT</entry>
       <entry>-5:00 </entry>
       <entry>Central Daylight Time</entry>
      </row>
      <row>
       <entry>EST</entry>
       <entry>-5:00 </entry>
       <entry>Eastern Standard Time</entry>
      </row>
      <row>
       <entry>ZP5</entry>
       <entry>-5:00</entry>
       <entry>GMT +5  hours</entry>
      </row>
      <row>
       <entry>CST</entry>
       <entry>-6:00 </entry>
       <entry>Central Std Time</entry>
      </row>
      <row>
       <entry>MDT</entry>
       <entry>-6:00</entry>
       <entry>Mountain Daylight Time</entry>
      </row>
      <row>
       <entry>ZP6</entry>
       <entry>-6:00</entry>
       <entry>GMT +6  hours</entry>
      </row>
      <row>
       <entry>MST</entry>
       <entry>-7:00</entry>
       <entry>Mountain Standard Time</entry>
      </row>
      <row>
       <entry>PDT</entry>
       <entry>-7:00</entry>
       <entry>Pacific Daylight Time</entry>
      </row>
      <row>
       <entry>PST</entry>
       <entry>-8:00</entry>
       <entry>Pacific Std Time</entry>
      </row>
      <row>
       <entry>YDT</entry>
       <entry>-8:00</entry>
       <entry>Yukon Daylight Time</entry>
      </row>
      <row>
       <entry>HDT</entry>
       <entry>-9:00</entry>
       <entry>Hawaii/Alaska Daylight Time</entry>
      </row>
      <row>
       <entry>YST</entry>
       <entry>-9:00</entry>
       <entry>Yukon Standard Time</entry>
      </row>
      <row>
       <entry>AHST</entry>
       <entry>-10:00 </entry>
       <entry>Alaska-Hawaii Std Time</entry>
      </row>
      <row>
       <entry>CAT</entry>
       <entry>-10:00 </entry>
       <entry>Central Alaska Time</entry>
      </row>
      <row>
       <entry>NT</entry>
       <entry>-11:00</entry>
       <entry>Nome Time</entry>
      </row>
      <row>
       <entry>IDLW</entry>
	 <entry>-12:00</entry>
       <entry>International Date Line, West</entry>
      </row>
     </tbody>
    </tgroup>
   </table>
   <note>
    <para>
     If the compiler option USE_AUSTRALIAN_RULES is set 
     then <literal>EST</literal> refers to Australia Eastern Std Time,
     which has an offset of +10:00 hours from UTC.
    </para>
   </note>
  </para>

  <para>
   Australian time zones and their naming variants
   account for fully one quarter of all time zones in the 
   <productname>Postgres</productname> time zone lookup table.
  </para>

  <procedure>
   <title>Date/Time Input Interpretation</title>

   <para>
    The date/time types are all decoded using a common set of routines.
   </para>

   <step>
    <para>
     Break the input string into tokens and categorize each token as
     a string, time, time zone, or number.
    </para>

    <substeps>
     <step>
      <para>
       If the token contains a colon (":"), this is a time string.
      </para>
     </step>

     <step>
      <para>
       If the token contains a dash ("-"), slash ("/"), or dot ("."),
       this is a date string which may have a text month.
      </para>
     </step>

     <step>
      <para>
       If the token is numeric only, then it is either a single field
       or an ISO-8601 concatenated date (e.g. "19990113" for January 13, 1999)
       or time (e.g. 141516 for 14:15:16).
      </para>
     </step>
     <step>
      <para>
       If the token starts with a plus ("+") or minus ("-"),
       then it is either a time zone or a special field.
      </para>
     </step>
    </substeps>
   </step>

   <step>
    <para>
     If the token is a text string, match up with possible strings.
    </para>
    
    <substeps>
     <step>
      <para>
       Do a binary-search table lookup for the token
       as either a special string (e.g. <literal>today</literal>),
       day (e.g. <literal>Thursday</literal>),
       month (e.g. <literal>January</literal>), or noise word (e.g. <literal>on</literal>).
      </para>
      <para>
       Set field values and bit mask for fields.
       For example, set year, month, day for <literal>today</literal>, and additionally
       hour, minute, second for <literal>now</literal>.
      </para>
     </step>
     
     <step>
      <para>
       If not found, do a similar binary-search table lookup to match
       the token with a time zone.
      </para>
     </step>

     <step>
      <para>
       If not found, throw an error.
      </para>
     </step>
    </substeps>
   </step>
   
   <step>
    <para>
     The token is a number or number field.
    </para>

    <substeps>
     <step>
      <para>
       If there are more than 4 digits, 
       and if no other date fields have been previously read, then interpret 
       as a "concatenated date" (e.g. <literal>19990118</literal>). 8
       and 6 digits are interpreted as year, month, and day, while 7
       and 5 digits are interpreted as year, day of year.
      </para>
     </step>

     <step>
      <para>
       If the token is three digits
       and a year has already been decoded, then interpret as day of year.
      </para>
     </step>
     
     <step>
      <para>
       If longer than two digits, then interpret as a year.
      </para>
     </step>

     <step>
      <para>
       If in European date mode, and if the day field has not yet been read,
       and if the value is less than or equal to 31, then interpret as a day.
      </para>
     </step>

     <step>
      <para>
       If in non-European (US) date mode, and if the month field has not yet been read,
       and if the value is less than or equal to 12, then interpret as a month.
      </para>
     </step>

     <step>
      <para>
       If the day field has not yet been read,
       and if the value is less than or equal to 31, then interpret as a month.
	</para>
       </step>

     <step>
      <para>
       If the month field has not yet been read,
       and if the value is less than or equal to 12, then interpret as a month.
      </para>
     </step>

     <step>
      <para>
       Otherwise, interpret as a year.
      </para>
     </step>
    </substeps>
   </step>

   <step>
    <para>
     If BC has been specified, negate the year and offset by one for
     internal storage
     (there is no year zero in the Gregorian calendar, so numerically
     1BC becomes year zero).
    </para>
   </step>

   <step>
    <para>
     If BC was not specified, and if the year field was two digits in length, then
     adjust the year to 4 digits. If the field was less than 70, then add 2000;
     otherwise, add 1900.

     <tip>
      <para>
       Gregorian years 1-99AD may be entered by using 4 digits with leading
       zeros (e.g. 0099 is 99AD). Three digits are also accepted as a
       year under most circumstances, though depending on position the
       numeric string may
       be interpreted as doy instead.
      </para>
     </tip>
    </para>
   </step>
  </procedure>
 </sect1>

 <sect1>
  <title>History</title>

  <note>
   <para>
    Contributed by 
    <ulink url="[e-mail]">Jos