func.sgml

关系型数据库 Postgresql 6.5.2

       </row>
       <row>
	<entry> reltime(timespan) </entry>
	<entry> reltime </entry>
	<entry> convert to reltime </entry>
	<entry> reltime('4 hrs'::timespan) </entry>
       </row>
       <row>
	<entry> timespan(reltime) </entry>
	<entry> timespan </entry>
	<entry> convert to timespan </entry>
	<entry> timespan('4 hours'::reltime) </entry>
       </row>
      </tbody>
     </tgroup>
    </table>
   </para>

   <para>
    For the
    <function>date_part</function> and <function>date_trunc</function>
    functions, arguments can be
    `year', `month', `day', `hour', `minute', and `second',
    as well as the more specialized quantities
    `decade', `century', `millenium', `millisecond', and `microsecond'.
    <function>date_part</function> allows `dow'
    to return day of week and `epoch' to return seconds since 1970
    (for <type>datetime</type>)
    or 'epoch' to return total elapsed seconds (for <type>timespan</type>).
   </para>
  </sect1>

  <sect1>
   <title>Geometric Functions</title>

   <para>
    The geometric types point, box, lseg, line, path, polygon, and
    circle have a large set of native support functions.
   </para>

   <para>
    <table tocentry="1">
     <title>Geometric Functions</title>
     <tgroup cols="4">
      <thead>
       <row>
	<entry>Function</entry>
	<entry>Returns</entry>
	<entry>Description</entry>
	<entry>Example</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry> area(box) </entry>
	<entry> float8 </entry>
	<entry> area of box </entry>
	<entry> area('((0,0),(1,1))'::box) </entry>
       </row>
       <row>
	<entry> area(circle) </entry>
	<entry> float8 </entry>
	<entry> area of circle </entry>
	<entry> area('((0,0),2.0)'::circle) </entry>
       </row>
       <row>
	<entry> box(box,box) </entry>
	<entry> box </entry>
	<entry> boxes to intersection box </entry>
	<entry> box('((0,0),(1,1))','((0.5,0.5),(2,2))') </entry>
       </row>
       <row>
	<entry> center(box) </entry>
	<entry> point </entry>
	<entry> center of object </entry>
	<entry> center('((0,0),(1,2))'::box) </entry>
       </row>
       <row>
	<entry> center(circle) </entry>
	<entry> point </entry>
	<entry> center of object </entry>
	<entry> center('((0,0),2.0)'::circle) </entry>
       </row>
       <row>
	<entry> diameter(circle) </entry>
	<entry> float8 </entry>
	<entry> diameter of circle </entry>
	<entry> diameter('((0,0),2.0)'::circle) </entry>
       </row>
       <row>
	<entry> height(box) </entry>
	<entry> float8 </entry>
	<entry> vertical size of box </entry>
	<entry> height('((0,0),(1,1))'::box) </entry>
       </row>
       <row>
	<entry> isclosed(path) </entry>
	<entry> bool </entry>
	<entry> a closed path? </entry>
	<entry> isclosed('((0,0),(1,1),(2,0))'::path) </entry>
       </row>
       <row>
	<entry> isopen(path) </entry>
	<entry> bool </entry>
	<entry> an open path? </entry>
	<entry> isopen('[(0,0),(1,1),(2,0)]'::path) </entry>
       </row>
       <row>
	<entry> length(lseg) </entry>
	<entry> float8 </entry>
	<entry> length of line segment </entry>
	<entry> length('((-1,0),(1,0))'::lseg) </entry>
       </row>
       <row>
	<entry> length(path) </entry>
	<entry> float8 </entry>
	<entry> length of path </entry>
	<entry> length('((0,0),(1,1),(2,0))'::path) </entry>
       </row>
       <row>
	<entry> pclose(path) </entry>
	<entry> path </entry>
	<entry> convert path to closed </entry>
	<entry> popen('[(0,0),(1,1),(2,0)]'::path) </entry>
       </row>
       <row>
	<entry> point(lseg,lseg) </entry>
	<entry> point </entry>
	<entry> intersection </entry>
	<entry> point('((-1,0),(1,0))'::lseg,'((-2,-2),(2,2))'::lseg) </entry>
       </row>
       <row>
	<entry> points(path) </entry>
	<entry> int4 </entry>
	<entry> number of points </entry>
	<entry> points('[(0,0),(1,1),(2,0)]'::path) </entry>
       </row>
       <row>
	<entry> popen(path) </entry>
	<entry> path </entry>
	<entry> convert path to open </entry>
	<entry> popen('((0,0),(1,1),(2,0))'::path) </entry>
       </row>
       <row>
	<entry> radius(circle) </entry>
	<entry> float8 </entry>
	<entry> radius of circle </entry>
	<entry> radius('((0,0),2.0)'::circle) </entry>
       </row>
       <row>
	<entry> width(box) </entry>
	<entry> float8 </entry>
	<entry> horizontal size </entry>
	<entry> width('((0,0),(1,1))'::box) </entry>
       </row>
      </tbody>
     </tgroup>
    </table>
   </para>

   <para>
    <table tocentry="1">
     <title>Geometric Type Conversion Functions</title>
     <tgroup cols="4">
      <thead>
       <row>
	<entry>Function</entry>
	<entry>Returns</entry>
	<entry>Description</entry>
	<entry>Example</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry> box(circle) </entry>
	<entry> box </entry>
	<entry> convert circle to box </entry>
	<entry> box('((0,0),2.0)'::circle) </entry>
       </row>
       <row>
	<entry> box(point,point) </entry>
	<entry> box </entry>
	<entry> convert points to box </entry>
	<entry> box('(0,0)'::point,'(1,1)'::point) </entry>
       </row>
       <row>
	<entry> box(polygon) </entry>
	<entry> box </entry>
	<entry> convert polygon to box </entry>
	<entry> box('((0,0),(1,1),(2,0))'::polygon) </entry>
       </row>
       <row>
	<entry> circle(box) </entry>
	<entry> circle </entry>
	<entry> convert to circle </entry>
	<entry> circle('((0,0),(1,1))'::box) </entry>
       </row>
       <row>
	<entry> circle(point,float8) </entry>
	<entry> circle </entry>
	<entry> convert to circle </entry>
	<entry> circle('(0,0)'::point,2.0) </entry>
       </row>
       <row>
	<entry> lseg(box) </entry>
	<entry> lseg </entry>
	<entry> convert diagonal to lseg </entry>
	<entry> lseg('((-1,0),(1,0))'::box) </entry>
       </row>
       <row>
	<entry> lseg(point,point) </entry>
	<entry> lseg </entry>
	<entry> convert to lseg </entry>
	<entry> lseg('(-1,0)'::point,'(1,0)'::point) </entry>
       </row>
       <row>
	<entry> path(polygon) </entry>
	<entry> point </entry>
	<entry> convert to path </entry>
	<entry> path('((0,0),(1,1),(2,0))'::polygon) </entry>
       </row>
       <row>
	<entry> point(circle) </entry>
	<entry> point </entry>
	<entry> convert to point (center) </entry>
	<entry> point('((0,0),2.0)'::circle) </entry>
       </row>
       <row>
	<entry> point(lseg,lseg) </entry>
	<entry> point </entry>
	<entry> convert to point (intersection) </entry>
	<entry> point('((-1,0),(1,0))'::lseg, '((-2,-2),(2,2))'::lseg) </entry>
       </row>
       <row>
	<entry> point(polygon) </entry>
	<entry> point </entry>
	<entry> center of polygon </entry>
	<entry> point('((0,0),(1,1),(2,0))'::polygon) </entry>
       </row>
       <row>
	<entry> polygon(box) </entry>
	<entry> polygon </entry>
	<entry> convert to polygon with 12 points </entry>
	<entry> polygon('((0,0),(1,1))'::box) </entry>
       </row>
       <row>
	<entry> polygon(circle) </entry>
	<entry> polygon </entry>
	<entry> convert to 12-point polygon </entry>
	<entry> polygon('((0,0),2.0)'::circle) </entry>
       </row>
       <row>
	<entry> polygon(<replaceable class="parameter">npts</replaceable>,circle) </entry>
	<entry> polygon </entry>
	<entry> convert to <replaceable class="parameter">npts</replaceable> polygon </entry>
	<entry> polygon(12,'((0,0),2.0)'::circle) </entry>
       </row>
       <row>
	<entry> polygon(path) </entry>
	<entry> polygon </entry>
	<entry> convert to polygon </entry>
	<entry> polygon('((0,0),(1,1),(2,0))'::path) </entry>
       </row>
      </tbody>
     </tgroup>
    </table>
   </para>

   <para>
    <table tocentry="1">
     <title>Geometric Upgrade Functions</title>
     <tgroup cols="4">
      <thead>
       <row>
	<entry>Function</entry>
	<entry>Returns</entry>
	<entry>Description</entry>
	<entry>Example</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry> isoldpath(path) </entry>
	<entry> path </entry>
	<entry> test path for pre-v6.1 form </entry>
	<entry> isoldpath('(1,3,0,0,1,1,2,0)'::path) </entry>
       </row>
       <row>
	<entry> revertpoly(polygon) </entry>
	<entry> polygon </entry>
	<entry> convert pre-v6.1 polygon </entry>
	<entry> revertpoly('((0,0),(1,1),(2,0))'::polygon) </entry>
       </row>
       <row>
	<entry> upgradepath(path) </entry>
	<entry> path </entry>
	<entry> convert pre-v6.1 path </entry>
	<entry> upgradepath('(1,3,0,0,1,1,2,0)'::path) </entry>
       </row>
       <row>
	<entry> upgradepoly(polygon) </entry>
	<entry> polygon </entry>
	<entry> convert pre-v6.1 polygon </entry>
	<entry> upgradepoly('(0,1,2,0,1,0)'::polygon) </entry>
       </row>
      </tbody>
     </tgroup>
    </table>
   </para>
  </sect1>

  <sect1>
   <title id="cidr-funcs">IP V4 Functions</title>

   <para>
    <table tocentry="1">
     <title><productname>Postgres</productname>IP V4 Functions</title>
     <tgroup cols="4">
      <thead>
       <row>
	<entry>Function</entry>
	<entry>Returns</entry>
	<entry>Description</entry>
	<entry>Example</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry> broadcast(cidr) </entry>
	<entry> text </entry>
	<entry> construct broadcast address as text </entry>
	<entry> broadcast('192.168.1.5/24') </entry>
       </row>
       <row>
	<entry> broadcast(inet) </entry>
	<entry> text </entry>
	<entry> construct broadcast address as text </entry>
	<entry> broadcast('192.168.1.5/24') </entry>
       </row>
       <row>
	<entry> host(inet) </entry>
	<entry> text </entry>
	<entry> extract host address as text </entry>
	<entry> host('192.168.1.5/24') </entry>
       </row>
       <row>
	<entry> masklen(cidr) </entry>
	<entry> int4 </entry>
	<entry> calculate netmask length </entry>
	<entry> masklen('192.168.1.5/24') </entry>
       </row>
       <row>
	<entry> masklen(inet) </entry>
	<entry> int4 </entry>
	<entry> calculate netmask length </entry>
	<entry> masklen('192.168.1.5/24') </entry>
       </row>
       <row>
	<entry> netmask(inet) </entry>
	<entry> text </entry>
	<entry> construct netmask as text </entry>
	<entry> netmask('192.168.1.5/24') </entry>
       </row>
      </tbody>
     </tgroup>
    </table>
   </para>

  </sect1>

 </chapter>

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