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PostgreSQL documentation

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</row>

<row>

<entry> # </entry>

<entry>Number of points in polygon</entry>

<entry>Number of points inpath orpolygon</entry>

<entry><literal># '((1,0),(0,1),(-1,0))'</literal></entry>

</row>

<row>

<entry>length of item</entry>

<entry><literal>length(path '((-1,0),(1,0))')</literal></entry>

</row>

<row>

<entry><function>npoints</function>(path)</entry>

<entry><type>integer</type></entry>

<entry>number of points</entry>

<entry><literal>npoints(path '[(0,0),(1,1),(2,0)]')</literal></entry>

</row>

<row>

<entry><function>npoints</function>(polygon)</entry>

<entry><type>integer</type></entry>

<entry>number of points</entry>

<entry><literal>npoints(polygon '((1,1),(0,0))')</literal></entry>

</row>

<row>

<entry><function>pclose</function>(path)</entry>

<entry><type>path</type></entry>

<entry><literal>point(lseg '((-1,0),(1,0))',lseg '((-2,-2),(2,2))')</literal></entry>

</row>

]]>

<row>

<entry><function>npoint</function>(path)</entry>

<entry><type>integer</type></entry>

<entry>number of points</entry>

<entry><literal>npoints(path '[(0,0),(1,1),(2,0)]')</literal></entry>

</row>

<row>

<entry><function>popen</function>(path)</entry>

<entry><type>path</type></entry>

<row>

<entry><function>polygon</function>(<type>box</type>)</entry>

<entry><type>polygon</type></entry>

<entry>12point polygon</entry>

<entry>4-point polygon</entry>

<entry><literal>polygon(box '((0,0),(1,1))')</literal></entry>

</row>

<row>

</tgroup>

</table>

<para>

It is possible to access the two component numbers of a <type>point</>

as though it were an array with subscripts 0,1. For example, if

<literal>t.p</> is a <type>point</> column then

<literal>SELECT p[0] FROM t</> retrieves the X coordinate;

<literal>UPDATE t SET p[1] = ...</> changes the Y coordinate.

In the same way, a <type>box</> or an <type>lseg</> may be treated

as an array of two <type>point</>s.

</para>

</sect1>