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D
porting hstore contrib module docs from postgres 8.4 (#3081)  
David Yozie 已提交
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
<topic id="topic_vcn_jkq_1bb">
 <title>hstore Functions</title>
 <body>
  <p>The <codeph>hstore</codeph> module implements a data type for storing sets of (key,value) pairs
   within a single Greenplum Database data field. This can be useful in various scenarios, such as
   rows with many attributes that are rarely examined, or semi-structured data.</p>
  <p>In the current implementation, neither the key nor the value string can exceed 65535 bytes in
   length; an error will be thrown if this limit is exceeded. These maximum lengths may change in
   future releases.</p>
  <section>
   <title>Installing hstore</title>
   <p>Before you can use <codeph>hstore</codeph> data type and functions, run the installation
    script <codeph>$GPHOME/share/postgresql/contrib/hstore.sql</codeph> in each database where you
    want the ability to query other
    databases:<codeblock>$ psql -d testdb -f $GPHOME/share/postgresql/contrib/hstore.sql</codeblock></p>
  </section>
  <section>
   <title>hstore External Representation</title>
   <p>The text representation of an <codeph>hstore</codeph> value includes zero or more
     <varname>key</varname>
    <codeph>=&gt;</codeph>
    <varname>value</varname> items, separated by commas. For example:
    <codeblock>k => v
foo => bar, baz => whatever
"1-a" => "anything at all"</codeblock> The order
    of the items is not considered significant (and may not be reproduced on output). Whitespace
    between items or around the <codeph>=&gt;</codeph> sign is ignored. Use double quotes if a key
    or value includes whitespace, comma, <codeph>=</codeph> or <codeph>&gt;</codeph>. To include a
    double quote or a backslash in a key or value, precede it with another backslash. (Keep in mind
    that depending on the setting of <varname>standard_conforming_strings</varname>, you may need to
    double backslashes in SQL literal strings.)</p>
   <p>A value (but not a key) can be a SQL NULL. This is represented as
    <codeblock>key => NULL</codeblock> The <codeph>NULL</codeph> keyword is not case-sensitive.
    Again, use double quotes if you want the string <codeph>null</codeph> to be treated as an
    ordinary data value.</p>
   <p>Currently, double quotes are always used to surround key and value strings on output, even
    when this is not strictly necessary.</p>
  </section>
  <section>
   <title>hstore Operators and Functions</title>
   <table id="hstore-op-table">
    <title>hstore Operators</title>
    <tgroup cols="4">
     <thead>
      <row>
       <entry>Operator</entry>
       <entry>Description</entry>
       <entry>Example</entry>
       <entry>Result</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry><codeph>hstore</codeph>
        <codeph>-&gt;</codeph>
        <codeph>text</codeph></entry>
       <entry>get value for key (null if not present)</entry>
       <entry><codeph>'a=&gt;x, b=&gt;y'::hstore -&gt; 'a'</codeph></entry>
       <entry><codeph>x</codeph></entry>
      </row>
      <row>
       <entry><codeph>text</codeph>
        <codeph>=&gt;</codeph>
        <codeph>text</codeph></entry>
       <entry>make single-item <codeph>hstore</codeph></entry>
       <entry><codeph>'a' =&gt; 'b'</codeph></entry>
       <entry><codeph>"a"=&gt;"b"</codeph></entry>
      </row>
      <row>
       <entry><codeph>hstore</codeph>
        <codeph>||</codeph>
        <codeph>hstore</codeph></entry>
       <entry>concatenation</entry>
       <entry><codeph>'a=&gt;b, c=&gt;d'::hstore || 'c=&gt;x, d=&gt;q'::hstore</codeph></entry>
       <entry><codeph>"a"=&gt;"b", "c"=&gt;"x", "d"=&gt;"q"</codeph></entry>
      </row>
      <row>
       <entry><codeph>hstore</codeph>
        <codeph>?</codeph>
        <codeph>text</codeph></entry>
       <entry>does <codeph>hstore</codeph> contain key?</entry>
       <entry><codeph>'a=&gt;1'::hstore ? 'a'</codeph></entry>
       <entry><codeph>t</codeph></entry>
      </row>
      <row>
       <entry><codeph>hstore</codeph>
        <codeph>@&gt;</codeph>
        <codeph>hstore</codeph></entry>
       <entry>does left operand contain right?</entry>
       <entry><codeph>'a=&gt;b, b=&gt;1, c=&gt;NULL'::hstore @&gt; 'b=&gt;1'</codeph></entry>
       <entry><codeph>t</codeph></entry>
      </row>
      <row>
       <entry><codeph>hstore</codeph>
        <codeph>&lt;@</codeph>
        <codeph>hstore</codeph></entry>
       <entry>is left operand contained in right?</entry>
       <entry><codeph>'a=&gt;c'::hstore &lt;@ 'a=&gt;b, b=&gt;1, c=&gt;NULL'</codeph></entry>
       <entry><codeph>f</codeph></entry>
      </row>
     </tbody>
    </tgroup>
   </table>
   <note>The <codeph>=&gt;</codeph> operator is deprecated and may be removed in a future release.
    Use the <codeph>hstore(text, text)</codeph> function instead.</note>
   <table id="hstore-func-table">
    <title>hstore Functions</title>
    <tgroup cols="5">
     <thead>
      <row>
       <entry>Function</entry>
       <entry>Return Type</entry>
       <entry>Description</entry>
       <entry>Example</entry>
       <entry>Result</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry><codeph>hstore(text, text)</codeph></entry>
       <entry><codeph>hstore</codeph></entry>
       <entry>make single-item <codeph>hstore</codeph></entry>
       <entry><codeph>hstore('a', 'b')</codeph></entry>
       <entry><codeph>"a"=&gt;"b"</codeph></entry>
      </row>
      <row>
       <entry><codeph>akeys(hstore)</codeph></entry>
       <entry><codeph>text[]</codeph></entry>
       <entry>get <codeph>hstore</codeph>'s keys as array</entry>
       <entry><codeph>akeys('a=&gt;1,b=&gt;2')</codeph></entry>
       <entry><codeph>{a,b}</codeph></entry>
      </row>
      <row>
       <entry><codeph>skeys(hstore)</codeph></entry>
       <entry><codeph>setof text</codeph></entry>
       <entry>get <codeph>hstore</codeph>'s keys as set</entry>
       <entry><codeph>skeys('a=&gt;1,b=&gt;2')</codeph></entry>
       <entry>
        <codeblock>a
b</codeblock>
       </entry>
      </row>
      <row>
       <entry><codeph>avals(hstore)</codeph></entry>
       <entry><codeph>text[]</codeph></entry>
       <entry>get <codeph>hstore</codeph>'s values as array</entry>
       <entry><codeph>avals('a=&gt;1,b=&gt;2')</codeph></entry>
       <entry><codeph>{1,2}</codeph></entry>
      </row>
      <row>
       <entry><codeph>svals(hstore)</codeph></entry>
       <entry><codeph>setof text</codeph></entry>
       <entry>get <codeph>hstore</codeph>'s values as set</entry>
       <entry><codeph>svals('a=&gt;1,b=&gt;2')</codeph></entry>
       <entry>
        <codeblock>1
2</codeblock>
       </entry>
      </row>
      <row>
       <entry><codeph>each(hstore)</codeph></entry>
       <entry><codeph>setof (key text, value text)</codeph></entry>
       <entry>get <codeph>hstore</codeph>'s keys and values as set</entry>
       <entry><codeph>select * from each('a=&gt;1,b=&gt;2')</codeph></entry>
       <entry>
        <codeblock> key | value
-----+-------
 a   | 1
 b   | 2</codeblock>
       </entry>
      </row>
      <row>
       <entry><codeph>exist(hstore,text)</codeph></entry>
       <entry><codeph>boolean</codeph></entry>
       <entry>does <codeph>hstore</codeph> contain key?</entry>
       <entry><codeph>exist('a=&gt;1','a')</codeph></entry>
       <entry><codeph>t</codeph></entry>
      </row>
      <row>
       <entry><codeph>defined(hstore,text)</codeph></entry>
       <entry><codeph>boolean</codeph></entry>
       <entry>does <codeph>hstore</codeph> contain non-null value for key?</entry>
       <entry><codeph>defined('a=&gt;NULL','a')</codeph></entry>
       <entry><codeph>f</codeph></entry>
      </row>
      <row>
       <entry><codeph>delete(hstore,text)</codeph></entry>
       <entry><codeph>hstore</codeph></entry>
       <entry>delete any item matching key</entry>
       <entry><codeph>delete('a=&gt;1,b=&gt;2','b')</codeph></entry>
       <entry><codeph>"a"=>"1"</codeph></entry>
      </row>
     </tbody>
    </tgroup>
   </table>
  </section>
  <section>
   <title>Indexes</title>
   <p><codeph>hstore</codeph> has index support for <codeph>@&gt;</codeph> and <codeph>?</codeph>
H
Enable GIN indexes.  
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    operators. You can use either GiST or GIN index types. For example:</p>
   <codeblock>
CREATE INDEX hidx ON testhstore USING GIST(h);

CREATE INDEX hidx ON testhstore USING GIN(h);
   </codeblock>
D
porting hstore contrib module docs from postgres 8.4 (#3081)  
David Yozie 已提交
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  </section>
  <section>
   <title>Examples</title>
   <p>Add a key, or update an existing key with a new value:</p>
   <codeblock>UPDATE tab SET h = h || ('c' => '3');</codeblock>
   <p>Delete a key:</p>
   <codeblock>UPDATE tab SET h = delete(h, 'k1');</codeblock>
  </section>
  <section>
   <title>Statistics</title>
   <p>The <codeph>hstore</codeph> type, because of its intrinsic liberality, could contain a lot of
    different keys. Checking for valid keys is the task of the application. Examples below
    demonstrate several techniques for checking keys and obtaining statistics.</p>
   <p>Simple example:</p>
   <codeblock>SELECT * FROM each('aaa=>bq, b=>NULL, ""=>1');</codeblock>
   <p>Using a table:</p>
   <codeblock>SELECT (each(h)).key, (each(h)).value INTO stat FROM testhstore;</codeblock>
   <p>Online statistics:</p>
   <codeblock>SELECT key, count(*) FROM
  (SELECT (each(h)).key FROM testhstore) AS stat
  GROUP BY key
  ORDER BY count DESC, key;
    key    | count
-----------+-------
 line      |   883
 query     |   207
 pos       |   203
 node      |   202
 space     |   197
 status    |   195
 public    |   194
 title     |   190
 org       |   189
...................</codeblock>
  </section>
 </body>
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</topic>