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- <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>F.16. hstore</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="fuzzystrmatch.html" title="F.15. fuzzystrmatch" /><link rel="next" href="intagg.html" title="F.17. intagg" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.16. hstore</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="fuzzystrmatch.html" title="F.15. fuzzystrmatch">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="intagg.html" title="F.17. intagg">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="HSTORE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.16. hstore</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="hstore.html#id-1.11.7.25.4">F.16.1. <code class="type">hstore</code> External Representation</a></span></dt><dt><span class="sect2"><a href="hstore.html#id-1.11.7.25.5">F.16.2. <code class="type">hstore</code> Operators and Functions</a></span></dt><dt><span class="sect2"><a href="hstore.html#id-1.11.7.25.6">F.16.3. Indexes</a></span></dt><dt><span class="sect2"><a href="hstore.html#id-1.11.7.25.7">F.16.4. Examples</a></span></dt><dt><span class="sect2"><a href="hstore.html#id-1.11.7.25.8">F.16.5. Statistics</a></span></dt><dt><span class="sect2"><a href="hstore.html#id-1.11.7.25.9">F.16.6. Compatibility</a></span></dt><dt><span class="sect2"><a href="hstore.html#id-1.11.7.25.10">F.16.7. Transforms</a></span></dt><dt><span class="sect2"><a href="hstore.html#id-1.11.7.25.11">F.16.8. Authors</a></span></dt></dl></div><a id="id-1.11.7.25.2" class="indexterm"></a><p>
- This module implements the <code class="type">hstore</code> data type for storing sets of
- key/value pairs within a single <span class="productname">PostgreSQL</span> value.
- This can be useful in various scenarios, such as rows with many attributes
- that are rarely examined, or semi-structured data. Keys and values are
- simply text strings.
- </p><div class="sect2" id="id-1.11.7.25.4"><div class="titlepage"><div><div><h3 class="title">F.16.1. <code class="type">hstore</code> External Representation</h3></div></div></div><p>
-
- The text representation of an <code class="type">hstore</code>, used for input and output,
- includes zero or more <em class="replaceable"><code>key</code></em> <code class="literal">=></code>
- <em class="replaceable"><code>value</code></em> pairs separated by commas. Some examples:
-
- </p><pre class="synopsis">
- k => v
- foo => bar, baz => whatever
- "1-a" => "anything at all"
- </pre><p>
-
- The order of the pairs is not significant (and may not be reproduced on
- output). Whitespace between pairs or around the <code class="literal">=></code> sign is
- ignored. Double-quote keys and values that include whitespace, commas,
- <code class="literal">=</code>s or <code class="literal">></code>s. To include a double quote or a
- backslash in a key or value, escape it with a backslash.
- </p><p>
- Each key in an <code class="type">hstore</code> is unique. If you declare an <code class="type">hstore</code>
- with duplicate keys, only one will be stored in the <code class="type">hstore</code> and
- there is no guarantee as to which will be kept:
-
- </p><pre class="programlisting">
- SELECT 'a=>1,a=>2'::hstore;
- hstore
- ----------
- "a"=>"1"
- </pre><p>
- </p><p>
- A value (but not a key) can be an SQL <code class="literal">NULL</code>. For example:
-
- </p><pre class="programlisting">
- key => NULL
- </pre><p>
-
- The <code class="literal">NULL</code> keyword is case-insensitive. Double-quote the
- <code class="literal">NULL</code> to treat it as the ordinary string <span class="quote">“<span class="quote">NULL</span>”</span>.
- </p><div class="note"><h3 class="title">Note</h3><p>
- Keep in mind that the <code class="type">hstore</code> text format, when used for input,
- applies <span class="emphasis"><em>before</em></span> any required quoting or escaping. If you are
- passing an <code class="type">hstore</code> literal via a parameter, then no additional
- processing is needed. But if you're passing it as a quoted literal
- constant, then any single-quote characters and (depending on the setting of
- the <code class="varname">standard_conforming_strings</code> configuration parameter)
- backslash characters need to be escaped correctly. See
- <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS" title="4.1.2.1. String Constants">Section 4.1.2.1</a> for more on the handling of string
- constants.
- </p></div><p>
- On output, double quotes always surround keys and values, even when it's
- not strictly necessary.
- </p></div><div class="sect2" id="id-1.11.7.25.5"><div class="titlepage"><div><div><h3 class="title">F.16.2. <code class="type">hstore</code> Operators and Functions</h3></div></div></div><p>
- The operators provided by the <code class="literal">hstore</code> module are
- shown in <a class="xref" href="hstore.html#HSTORE-OP-TABLE" title="Table F.7. hstore Operators">Table F.7</a>, the functions
- in <a class="xref" href="hstore.html#HSTORE-FUNC-TABLE" title="Table F.8. hstore Functions">Table F.8</a>.
- </p><div class="table" id="HSTORE-OP-TABLE"><p class="title"><strong>Table F.7. <code class="type">hstore</code> Operators</strong></p><div class="table-contents"><table class="table" summary="hstore Operators" border="1"><colgroup><col /><col /><col /><col /></colgroup><thead><tr><th>Operator</th><th>Description</th><th>Example</th><th>Result</th></tr></thead><tbody><tr><td><code class="type">hstore</code> <code class="literal">-></code> <code class="type">text</code></td><td>get value for key (<code class="literal">NULL</code> if not present)</td><td><code class="literal">'a=>x, b=>y'::hstore -> 'a'</code></td><td><code class="literal">x</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">-></code> <code class="type">text[]</code></td><td>get values for keys (<code class="literal">NULL</code> if not present)</td><td><code class="literal">'a=>x, b=>y, c=>z'::hstore -> ARRAY['c','a']</code></td><td><code class="literal">{"z","x"}</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">||</code> <code class="type">hstore</code></td><td>concatenate <code class="type">hstore</code>s</td><td><code class="literal">'a=>b, c=>d'::hstore || 'c=>x, d=>q'::hstore</code></td><td><code class="literal">"a"=>"b", "c"=>"x", "d"=>"q"</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">?</code> <code class="type">text</code></td><td>does <code class="type">hstore</code> contain key?</td><td><code class="literal">'a=>1'::hstore ? 'a'</code></td><td><code class="literal">t</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">?&</code> <code class="type">text[]</code></td><td>does <code class="type">hstore</code> contain all specified keys?</td><td><code class="literal">'a=>1,b=>2'::hstore ?& ARRAY['a','b']</code></td><td><code class="literal">t</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">?|</code> <code class="type">text[]</code></td><td>does <code class="type">hstore</code> contain any of the specified keys?</td><td><code class="literal">'a=>1,b=>2'::hstore ?| ARRAY['b','c']</code></td><td><code class="literal">t</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">@></code> <code class="type">hstore</code></td><td>does left operand contain right?</td><td><code class="literal">'a=>b, b=>1, c=>NULL'::hstore @> 'b=>1'</code></td><td><code class="literal">t</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal"><@</code> <code class="type">hstore</code></td><td>is left operand contained in right?</td><td><code class="literal">'a=>c'::hstore <@ 'a=>b, b=>1, c=>NULL'</code></td><td><code class="literal">f</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">-</code> <code class="type">text</code></td><td>delete key from left operand</td><td><code class="literal">'a=>1, b=>2, c=>3'::hstore - 'b'::text</code></td><td><code class="literal">"a"=>"1", "c"=>"3"</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">-</code> <code class="type">text[]</code></td><td>delete keys from left operand</td><td><code class="literal">'a=>1, b=>2, c=>3'::hstore - ARRAY['a','b']</code></td><td><code class="literal">"c"=>"3"</code></td></tr><tr><td><code class="type">hstore</code> <code class="literal">-</code> <code class="type">hstore</code></td><td>delete matching pairs from left operand</td><td><code class="literal">'a=>1, b=>2, c=>3'::hstore - 'a=>4, b=>2'::hstore</code></td><td><code class="literal">"a"=>"1", "c"=>"3"</code></td></tr><tr><td><code class="type">record</code> <code class="literal">#=</code> <code class="type">hstore</code></td><td>replace fields in <code class="type">record</code> with matching values from <code class="type">hstore</code></td><td>see Examples section</td><td> </td></tr><tr><td><code class="literal">%%</code> <code class="type">hstore</code></td><td>convert <code class="type">hstore</code> to array of alternating keys and values</td><td><code class="literal">%% 'a=>foo, b=>bar'::hstore</code></td><td><code class="literal">{a,foo,b,bar}</code></td></tr><tr><td><code class="literal">%#</code> <code class="type">hstore</code></td><td>convert <code class="type">hstore</code> to two-dimensional key/value array</td><td><code class="literal">%# 'a=>foo, b=>bar'::hstore</code></td><td><code class="literal">{{a,foo},{b,bar}}</code></td></tr></tbody></table></div></div><br class="table-break" /><div class="note"><h3 class="title">Note</h3><p>
- Prior to PostgreSQL 8.2, the containment operators <code class="literal">@></code>
- and <code class="literal"><@</code> were called <code class="literal">@</code> and <code class="literal">~</code>,
- respectively. These names are still available, but are deprecated and will
- eventually be removed. Notice that the old names are reversed from the
- convention formerly followed by the core geometric data types!
- </p></div><div class="table" id="HSTORE-FUNC-TABLE"><p class="title"><strong>Table F.8. <code class="type">hstore</code> Functions</strong></p><div class="table-contents"><table class="table" summary="hstore Functions" border="1"><colgroup><col /><col /><col /><col /><col /></colgroup><thead><tr><th>Function</th><th>Return Type</th><th>Description</th><th>Example</th><th>Result</th></tr></thead><tbody><tr><td><code class="function">hstore(record)</code><a id="id-1.11.7.25.5.5.2.2.1.1.2" class="indexterm"></a></td><td><code class="type">hstore</code></td><td>construct an <code class="type">hstore</code> from a record or row</td><td><code class="literal">hstore(ROW(1,2))</code></td><td><code class="literal">f1=>1,f2=>2</code></td></tr><tr><td><code class="function">hstore(text[])</code></td><td><code class="type">hstore</code></td><td>construct an <code class="type">hstore</code> from an array, which may be either
- a key/value array, or a two-dimensional array</td><td><code class="literal">hstore(ARRAY['a','1','b','2']) || hstore(ARRAY[['c','3'],['d','4']])</code></td><td><code class="literal">a=>1, b=>2, c=>3, d=>4</code></td></tr><tr><td><code class="function">hstore(text[], text[])</code></td><td><code class="type">hstore</code></td><td>construct an <code class="type">hstore</code> from separate key and value arrays</td><td><code class="literal">hstore(ARRAY['a','b'], ARRAY['1','2'])</code></td><td><code class="literal">"a"=>"1","b"=>"2"</code></td></tr><tr><td><code class="function">hstore(text, text)</code></td><td><code class="type">hstore</code></td><td>make single-item <code class="type">hstore</code></td><td><code class="literal">hstore('a', 'b')</code></td><td><code class="literal">"a"=>"b"</code></td></tr><tr><td><code class="function">akeys(hstore)</code><a id="id-1.11.7.25.5.5.2.2.5.1.2" class="indexterm"></a></td><td><code class="type">text[]</code></td><td>get <code class="type">hstore</code>'s keys as an array</td><td><code class="literal">akeys('a=>1,b=>2')</code></td><td><code class="literal">{a,b}</code></td></tr><tr><td><code class="function">skeys(hstore)</code><a id="id-1.11.7.25.5.5.2.2.6.1.2" class="indexterm"></a></td><td><code class="type">setof text</code></td><td>get <code class="type">hstore</code>'s keys as a set</td><td><code class="literal">skeys('a=>1,b=>2')</code></td><td>
- <pre class="programlisting">
- a
- b
- </pre></td></tr><tr><td><code class="function">avals(hstore)</code><a id="id-1.11.7.25.5.5.2.2.7.1.2" class="indexterm"></a></td><td><code class="type">text[]</code></td><td>get <code class="type">hstore</code>'s values as an array</td><td><code class="literal">avals('a=>1,b=>2')</code></td><td><code class="literal">{1,2}</code></td></tr><tr><td><code class="function">svals(hstore)</code><a id="id-1.11.7.25.5.5.2.2.8.1.2" class="indexterm"></a></td><td><code class="type">setof text</code></td><td>get <code class="type">hstore</code>'s values as a set</td><td><code class="literal">svals('a=>1,b=>2')</code></td><td>
- <pre class="programlisting">
- 1
- 2
- </pre></td></tr><tr><td><code class="function">hstore_to_array(hstore)</code><a id="id-1.11.7.25.5.5.2.2.9.1.2" class="indexterm"></a></td><td><code class="type">text[]</code></td><td>get <code class="type">hstore</code>'s keys and values as an array of alternating
- keys and values</td><td><code class="literal">hstore_to_array('a=>1,b=>2')</code></td><td><code class="literal">{a,1,b,2}</code></td></tr><tr><td><code class="function">hstore_to_matrix(hstore)</code><a id="id-1.11.7.25.5.5.2.2.10.1.2" class="indexterm"></a></td><td><code class="type">text[]</code></td><td>get <code class="type">hstore</code>'s keys and values as a two-dimensional array</td><td><code class="literal">hstore_to_matrix('a=>1,b=>2')</code></td><td><code class="literal">{{a,1},{b,2}}</code></td></tr><tr><td><code class="function">hstore_to_json(hstore)</code><a id="id-1.11.7.25.5.5.2.2.11.1.2" class="indexterm"></a></td><td><code class="type">json</code></td><td>get <code class="type">hstore</code> as a <code class="type">json</code> value, converting
- all non-null values to JSON strings</td><td><code class="literal">hstore_to_json('"a key"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>2.345e+4')</code></td><td><code class="literal">{"a key": "1", "b": "t", "c": null, "d": "12345", "e": "012345", "f": "1.234", "g": "2.345e+4"}</code></td></tr><tr><td><code class="function">hstore_to_jsonb(hstore)</code><a id="id-1.11.7.25.5.5.2.2.12.1.2" class="indexterm"></a></td><td><code class="type">jsonb</code></td><td>get <code class="type">hstore</code> as a <code class="type">jsonb</code> value, converting
- all non-null values to JSON strings</td><td><code class="literal">hstore_to_jsonb('"a key"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>2.345e+4')</code></td><td><code class="literal">{"a key": "1", "b": "t", "c": null, "d": "12345", "e": "012345", "f": "1.234", "g": "2.345e+4"}</code></td></tr><tr><td><code class="function">hstore_to_json_loose(hstore)</code><a id="id-1.11.7.25.5.5.2.2.13.1.2" class="indexterm"></a></td><td><code class="type">json</code></td><td>get <code class="type">hstore</code> as a <code class="type">json</code> value, but attempt to distinguish numerical and Boolean values so they are unquoted in the JSON</td><td><code class="literal">hstore_to_json_loose('"a key"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>2.345e+4')</code></td><td><code class="literal">{"a key": 1, "b": true, "c": null, "d": 12345, "e": "012345", "f": 1.234, "g": 2.345e+4}</code></td></tr><tr><td><code class="function">hstore_to_jsonb_loose(hstore)</code><a id="id-1.11.7.25.5.5.2.2.14.1.2" class="indexterm"></a></td><td><code class="type">jsonb</code></td><td>get <code class="type">hstore</code> as a <code class="type">jsonb</code> value, but attempt to distinguish numerical and Boolean values so they are unquoted in the JSON</td><td><code class="literal">hstore_to_jsonb_loose('"a key"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>2.345e+4')</code></td><td><code class="literal">{"a key": 1, "b": true, "c": null, "d": 12345, "e": "012345", "f": 1.234, "g": 2.345e+4}</code></td></tr><tr><td><code class="function">slice(hstore, text[])</code><a id="id-1.11.7.25.5.5.2.2.15.1.2" class="indexterm"></a></td><td><code class="type">hstore</code></td><td>extract a subset of an <code class="type">hstore</code></td><td><code class="literal">slice('a=>1,b=>2,c=>3'::hstore, ARRAY['b','c','x'])</code></td><td><code class="literal">"b"=>"2", "c"=>"3"</code></td></tr><tr><td><code class="function">each(hstore)</code><a id="id-1.11.7.25.5.5.2.2.16.1.2" class="indexterm"></a></td><td><code class="type">setof(key text, value text)</code></td><td>get <code class="type">hstore</code>'s keys and values as a set</td><td><code class="literal">select * from each('a=>1,b=>2')</code></td><td>
- <pre class="programlisting">
- key | value
- -----+-------
- a | 1
- b | 2
- </pre></td></tr><tr><td><code class="function">exist(hstore,text)</code><a id="id-1.11.7.25.5.5.2.2.17.1.2" class="indexterm"></a></td><td><code class="type">boolean</code></td><td>does <code class="type">hstore</code> contain key?</td><td><code class="literal">exist('a=>1','a')</code></td><td><code class="literal">t</code></td></tr><tr><td><code class="function">defined(hstore,text)</code><a id="id-1.11.7.25.5.5.2.2.18.1.2" class="indexterm"></a></td><td><code class="type">boolean</code></td><td>does <code class="type">hstore</code> contain non-<code class="literal">NULL</code> value for key?</td><td><code class="literal">defined('a=>NULL','a')</code></td><td><code class="literal">f</code></td></tr><tr><td><code class="function">delete(hstore,text)</code><a id="id-1.11.7.25.5.5.2.2.19.1.2" class="indexterm"></a></td><td><code class="type">hstore</code></td><td>delete pair with matching key</td><td><code class="literal">delete('a=>1,b=>2','b')</code></td><td><code class="literal">"a"=>"1"</code></td></tr><tr><td><code class="function">delete(hstore,text[])</code></td><td><code class="type">hstore</code></td><td>delete pairs with matching keys</td><td><code class="literal">delete('a=>1,b=>2,c=>3',ARRAY['a','b'])</code></td><td><code class="literal">"c"=>"3"</code></td></tr><tr><td><code class="function">delete(hstore,hstore)</code></td><td><code class="type">hstore</code></td><td>delete pairs matching those in the second argument</td><td><code class="literal">delete('a=>1,b=>2','a=>4,b=>2'::hstore)</code></td><td><code class="literal">"a"=>"1"</code></td></tr><tr><td><code class="function">populate_record(record,hstore)</code><a id="id-1.11.7.25.5.5.2.2.22.1.2" class="indexterm"></a></td><td><code class="type">record</code></td><td>replace fields in <code class="type">record</code> with matching values from <code class="type">hstore</code></td><td>see Examples section</td><td> </td></tr></tbody></table></div></div><br class="table-break" /><div class="note"><h3 class="title">Note</h3><p>
- The function <code class="function">hstore_to_json</code> is used when
- an <code class="type">hstore</code> value is cast to <code class="type">json</code>.
- Likewise, <code class="function">hstore_to_jsonb</code> is used when
- an <code class="type">hstore</code> value is cast to <code class="type">jsonb</code>.
- </p></div><div class="note"><h3 class="title">Note</h3><p>
- The function <code class="function">populate_record</code> is actually declared
- with <code class="type">anyelement</code>, not <code class="type">record</code>, as its first argument,
- but it will reject non-record types with a run-time error.
- </p></div></div><div class="sect2" id="id-1.11.7.25.6"><div class="titlepage"><div><div><h3 class="title">F.16.3. Indexes</h3></div></div></div><p>
- <code class="type">hstore</code> has GiST and GIN index support for the <code class="literal">@></code>,
- <code class="literal">?</code>, <code class="literal">?&</code> and <code class="literal">?|</code> operators. For example:
- </p><pre class="programlisting">
- CREATE INDEX hidx ON testhstore USING GIST (h);
-
- CREATE INDEX hidx ON testhstore USING GIN (h);
- </pre><p>
- <code class="type">hstore</code> also supports <code class="type">btree</code> or <code class="type">hash</code> indexes for
- the <code class="literal">=</code> operator. This allows <code class="type">hstore</code> columns to be
- declared <code class="literal">UNIQUE</code>, or to be used in <code class="literal">GROUP BY</code>,
- <code class="literal">ORDER BY</code> or <code class="literal">DISTINCT</code> expressions. The sort ordering
- for <code class="type">hstore</code> values is not particularly useful, but these indexes
- may be useful for equivalence lookups. Create indexes for <code class="literal">=</code>
- comparisons as follows:
- </p><pre class="programlisting">
- CREATE INDEX hidx ON testhstore USING BTREE (h);
-
- CREATE INDEX hidx ON testhstore USING HASH (h);
- </pre></div><div class="sect2" id="id-1.11.7.25.7"><div class="titlepage"><div><div><h3 class="title">F.16.4. Examples</h3></div></div></div><p>
- Add a key, or update an existing key with a new value:
- </p><pre class="programlisting">
- UPDATE tab SET h = h || hstore('c', '3');
- </pre><p>
- </p><p>
- Delete a key:
- </p><pre class="programlisting">
- UPDATE tab SET h = delete(h, 'k1');
- </pre><p>
- </p><p>
- Convert a <code class="type">record</code> to an <code class="type">hstore</code>:
- </p><pre class="programlisting">
- CREATE TABLE test (col1 integer, col2 text, col3 text);
- INSERT INTO test VALUES (123, 'foo', 'bar');
-
- SELECT hstore(t) FROM test AS t;
- hstore
- ---------------------------------------------
- "col1"=>"123", "col2"=>"foo", "col3"=>"bar"
- (1 row)
- </pre><p>
- </p><p>
- Convert an <code class="type">hstore</code> to a predefined <code class="type">record</code> type:
- </p><pre class="programlisting">
- CREATE TABLE test (col1 integer, col2 text, col3 text);
-
- SELECT * FROM populate_record(null::test,
- '"col1"=>"456", "col2"=>"zzz"');
- col1 | col2 | col3
- ------+------+------
- 456 | zzz |
- (1 row)
- </pre><p>
- </p><p>
- Modify an existing record using the values from an <code class="type">hstore</code>:
- </p><pre class="programlisting">
- CREATE TABLE test (col1 integer, col2 text, col3 text);
- INSERT INTO test VALUES (123, 'foo', 'bar');
-
- SELECT (r).* FROM (SELECT t #= '"col3"=>"baz"' AS r FROM test t) s;
- col1 | col2 | col3
- ------+------+------
- 123 | foo | baz
- (1 row)
- </pre><p>
- </p></div><div class="sect2" id="id-1.11.7.25.8"><div class="titlepage"><div><div><h3 class="title">F.16.5. Statistics</h3></div></div></div><p>
- The <code class="type">hstore</code> type, because of its intrinsic liberality, could
- contain a lot of different keys. Checking for valid keys is the task of the
- application. The following examples demonstrate several techniques for
- checking keys and obtaining statistics.
- </p><p>
- Simple example:
- </p><pre class="programlisting">
- SELECT * FROM each('aaa=>bq, b=>NULL, ""=>1');
- </pre><p>
- </p><p>
- Using a table:
- </p><pre class="programlisting">
- SELECT (each(h)).key, (each(h)).value INTO stat FROM testhstore;
- </pre><p>
- </p><p>
- Online statistics:
- </p><pre class="programlisting">
- 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
- ...................
- </pre><p>
- </p></div><div class="sect2" id="id-1.11.7.25.9"><div class="titlepage"><div><div><h3 class="title">F.16.6. Compatibility</h3></div></div></div><p>
- As of PostgreSQL 9.0, <code class="type">hstore</code> uses a different internal
- representation than previous versions. This presents no obstacle for
- dump/restore upgrades since the text representation (used in the dump) is
- unchanged.
- </p><p>
- In the event of a binary upgrade, upward compatibility is maintained by
- having the new code recognize old-format data. This will entail a slight
- performance penalty when processing data that has not yet been modified by
- the new code. It is possible to force an upgrade of all values in a table
- column by doing an <code class="literal">UPDATE</code> statement as follows:
- </p><pre class="programlisting">
- UPDATE tablename SET hstorecol = hstorecol || '';
- </pre><p>
- </p><p>
- Another way to do it is:
- </p><pre class="programlisting">
- ALTER TABLE tablename ALTER hstorecol TYPE hstore USING hstorecol || '';
- </pre><p>
- The <code class="command">ALTER TABLE</code> method requires an exclusive lock on the table,
- but does not result in bloating the table with old row versions.
- </p></div><div class="sect2" id="id-1.11.7.25.10"><div class="titlepage"><div><div><h3 class="title">F.16.7. Transforms</h3></div></div></div><p>
- Additional extensions are available that implement transforms for
- the <code class="type">hstore</code> type for the languages PL/Perl and PL/Python. The
- extensions for PL/Perl are called <code class="literal">hstore_plperl</code>
- and <code class="literal">hstore_plperlu</code>, for trusted and untrusted PL/Perl.
- If you install these transforms and specify them when creating a
- function, <code class="type">hstore</code> values are mapped to Perl hashes. The
- extensions for PL/Python are
- called <code class="literal">hstore_plpythonu</code>, <code class="literal">hstore_plpython2u</code>,
- and <code class="literal">hstore_plpython3u</code>
- (see <a class="xref" href="plpython-python23.html" title="45.1. Python 2 vs. Python 3">Section 45.1</a> for the PL/Python naming
- convention). If you use them, <code class="type">hstore</code> values are mapped to
- Python dictionaries.
- </p><div class="caution"><h3 class="title">Caution</h3><p>
- It is strongly recommended that the transform extensions be installed in
- the same schema as <code class="filename">hstore</code>. Otherwise there are
- installation-time security hazards if a transform extension's schema
- contains objects defined by a hostile user.
- </p></div></div><div class="sect2" id="id-1.11.7.25.11"><div class="titlepage"><div><div><h3 class="title">F.16.8. Authors</h3></div></div></div><p>
- Oleg Bartunov <code class="email"><<a class="email" href="mailto:oleg@sai.msu.su">oleg@sai.msu.su</a>></code>, Moscow, Moscow University, Russia
- </p><p>
- Teodor Sigaev <code class="email"><<a class="email" href="mailto:teodor@sigaev.ru">teodor@sigaev.ru</a>></code>, Moscow, Delta-Soft Ltd., Russia
- </p><p>
- Additional enhancements by Andrew Gierth <code class="email"><<a class="email" href="mailto:andrew@tao11.riddles.org.uk">andrew@tao11.riddles.org.uk</a>></code>,
- United Kingdom
- </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="fuzzystrmatch.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="intagg.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.15. fuzzystrmatch </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> F.17. intagg</td></tr></table></div></body></html>
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