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<div class="sect1" id="HSTORE">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">F.17. hstore — hstore key/value datatype <a class="id_link" href="#HSTORE">#</a></h2>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt><span class="sect2"><a href="/docs/current/hstore.html#HSTORE-EXTERNAL-REP">F.17.1. <code class="type">hstore</code> External Representation</a></span></dt>
<dt><span class="sect2"><a href="/docs/current/hstore.html#HSTORE-OPS-FUNCS">F.17.2. <code class="type">hstore</code> Operators and Functions</a></span></dt>
<dt><span class="sect2"><a href="/docs/current/hstore.html#HSTORE-INDEXES">F.17.3. Indexes</a></span></dt>
<dt><span class="sect2"><a href="/docs/current/hstore.html#HSTORE-EXAMPLES">F.17.4. Examples</a></span></dt>
<dt><span class="sect2"><a href="/docs/current/hstore.html#HSTORE-STATISTICS">F.17.5. Statistics</a></span></dt>
<dt><span class="sect2"><a href="/docs/current/hstore.html#HSTORE-COMPATIBILITY">F.17.6. Compatibility</a></span></dt>
<dt><span class="sect2"><a href="/docs/current/hstore.html#HSTORE-TRANSFORMS">F.17.7. Transforms</a></span></dt>
<dt><span class="sect2"><a href="/docs/current/hstore.html#HSTORE-AUTHORS">F.17.8. Authors</a></span></dt>
</dl>
</div><a class="indexterm" id="id-1.11.7.27.2" name="id-1.11.7.27.2"></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>
<p>This module is considered <span class="quote">“<span class="quote">trusted</span>”</span>, that is, it can be installed by non-superusers who have <code class="literal">CREATE</code> privilege on the current database.</p>
<div class="sect2" id="HSTORE-EXTERNAL-REP">
<div class="titlepage">
<div>
<div>
<h3 class="title">F.17.1. <code class="type">hstore</code> External Representation <a class="id_link" href="#HSTORE-EXTERNAL-REP">#</a></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">=&gt;</code> <em class="replaceable"><code>value</code></em> pairs separated by commas. Some examples:</p>
<pre class="synopsis">k =&gt; v
foo =&gt; bar, baz =&gt; whatever
"1-a" =&gt; "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">=&gt;</code> sign is ignored. Double-quote keys and values that include whitespace, commas, <code class="literal">=</code>s or <code class="literal">&gt;</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=&gt;1,a=&gt;2'::hstore;
  hstore
----------
 "a"=&gt;"1"
</pre>
<p>A value (but not a key) can be an SQL <code class="literal">NULL</code>. For example:</p>
<pre class="programlisting">key =&gt; 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="/docs/current/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="HSTORE-OPS-FUNCS">
<div class="titlepage">
<div>
<div>
<h3 class="title">F.17.2. <code class="type">hstore</code> Operators and Functions <a class="id_link" href="#HSTORE-OPS-FUNCS">#</a></h3>
</div>
</div>
</div>
<p>The operators provided by the <code class="literal">hstore</code> module are shown in <a class="xref" href="/docs/current/hstore.html#HSTORE-OP-TABLE" title="Table F.6. hstore Operators">Table F.6</a>, the functions in <a class="xref" href="/docs/current/hstore.html#HSTORE-FUNC-TABLE" title="Table F.7. hstore Functions">Table F.7</a>.</p>
<div class="table" id="HSTORE-OP-TABLE">
<p class="title"><strong>Table F.6. <code class="type">hstore</code> Operators</strong></p>
<div class="table-contents">
<table border="1" class="table" summary="hstore Operators">
<colgroup>
<col/>
</colgroup>
<thead>
<tr>
<th class="func_table_entry">
<p class="func_signature">Operator</p>
<p>Description</p>
<p>Example(s)</p>
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">-&gt;</code> <code class="type">text</code> → <code class="returnvalue">text</code></p>
<p>Returns value associated with given key, or <code class="literal">NULL</code> if not present.</p>
<p><code class="literal">'a=&gt;x, b=&gt;y'::hstore -&gt; 'a'</code> → <code class="returnvalue">x</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">-&gt;</code> <code class="type">text[]</code> → <code class="returnvalue">text[]</code></p>
<p>Returns values associated with given keys, or <code class="literal">NULL</code> if not present.</p>
<p><code class="literal">'a=&gt;x, b=&gt;y, c=&gt;z'::hstore -&gt; ARRAY['c','a']</code> → <code class="returnvalue">{"z","x"}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">||</code> <code class="type">hstore</code> → <code class="returnvalue">hstore</code></p>
<p>Concatenates two <code class="type">hstore</code>s.</p>
<p><code class="literal">'a=&gt;b, c=&gt;d'::hstore || 'c=&gt;x, d=&gt;q'::hstore</code> → <code class="returnvalue">"a"=&gt;"b", "c"=&gt;"x", "d"=&gt;"q"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">?</code> <code class="type">text</code> → <code class="returnvalue">boolean</code></p>
<p>Does <code class="type">hstore</code> contain key?</p>
<p><code class="literal">'a=&gt;1'::hstore ? 'a'</code> → <code class="returnvalue">t</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">?&amp;</code> <code class="type">text[]</code> → <code class="returnvalue">boolean</code></p>
<p>Does <code class="type">hstore</code> contain all the specified keys?</p>
<p><code class="literal">'a=&gt;1,b=&gt;2'::hstore ?&amp; ARRAY['a','b']</code> → <code class="returnvalue">t</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">?|</code> <code class="type">text[]</code> → <code class="returnvalue">boolean</code></p>
<p>Does <code class="type">hstore</code> contain any of the specified keys?</p>
<p><code class="literal">'a=&gt;1,b=&gt;2'::hstore ?| ARRAY['b','c']</code> → <code class="returnvalue">t</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">@&gt;</code> <code class="type">hstore</code> → <code class="returnvalue">boolean</code></p>
<p>Does left operand contain right?</p>
<p><code class="literal">'a=&gt;b, b=&gt;1, c=&gt;NULL'::hstore @&gt; 'b=&gt;1'</code> → <code class="returnvalue">t</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">&lt;@</code> <code class="type">hstore</code> → <code class="returnvalue">boolean</code></p>
<p>Is left operand contained in right?</p>
<p><code class="literal">'a=&gt;c'::hstore &lt;@ 'a=&gt;b, b=&gt;1, c=&gt;NULL'</code> → <code class="returnvalue">f</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">-</code> <code class="type">text</code> → <code class="returnvalue">hstore</code></p>
<p>Deletes key from left operand.</p>
<p><code class="literal">'a=&gt;1, b=&gt;2, c=&gt;3'::hstore - 'b'::text</code> → <code class="returnvalue">"a"=&gt;"1", "c"=&gt;"3"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">-</code> <code class="type">text[]</code> → <code class="returnvalue">hstore</code></p>
<p>Deletes keys from left operand.</p>
<p><code class="literal">'a=&gt;1, b=&gt;2, c=&gt;3'::hstore - ARRAY['a','b']</code> → <code class="returnvalue">"c"=&gt;"3"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">hstore</code> <code class="literal">-</code> <code class="type">hstore</code> → <code class="returnvalue">hstore</code></p>
<p>Deletes pairs from left operand that match pairs in the right operand.</p>
<p><code class="literal">'a=&gt;1, b=&gt;2, c=&gt;3'::hstore - 'a=&gt;4, b=&gt;2'::hstore</code> → <code class="returnvalue">"a"=&gt;"1", "c"=&gt;"3"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="type">anyelement</code> <code class="literal">#=</code> <code class="type">hstore</code> → <code class="returnvalue">anyelement</code></p>
<p>Replaces fields in the left operand (which must be a composite type) with matching values from <code class="type">hstore</code>.</p>
<p><code class="literal">ROW(1,3) #= 'f1=&gt;11'::hstore</code> → <code class="returnvalue">(11,3)</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="literal">%%</code> <code class="type">hstore</code> → <code class="returnvalue">text[]</code></p>
<p>Converts <code class="type">hstore</code> to an array of alternating keys and values.</p>
<p><code class="literal">%% 'a=&gt;foo, b=&gt;bar'::hstore</code> → <code class="returnvalue">{a,foo,b,bar}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="literal">%#</code> <code class="type">hstore</code> → <code class="returnvalue">text[]</code></p>
<p>Converts <code class="type">hstore</code> to a two-dimensional key/value array.</p>
<p><code class="literal">%# 'a=&gt;foo, b=&gt;bar'::hstore</code> → <code class="returnvalue">{{a,foo},{b,bar}}</code></p>
</td>
</tr>
</tbody>
</table>
</div>
</div><br class="table-break"/>
<div class="table" id="HSTORE-FUNC-TABLE">
<p class="title"><strong>Table F.7. <code class="type">hstore</code> Functions</strong></p>
<div class="table-contents">
<table border="1" class="table" summary="hstore Functions">
<colgroup>
<col/>
</colgroup>
<thead>
<tr>
<th class="func_table_entry">
<p class="func_signature">Function</p>
<p>Description</p>
<p>Example(s)</p>
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.1.1.1.1" name="id-1.11.7.27.6.4.2.2.1.1.1.1"></a> <code class="function">hstore</code> ( <code class="type">record</code> ) → <code class="returnvalue">hstore</code></p>
<p>Constructs an <code class="type">hstore</code> from a record or row.</p>
<p><code class="literal">hstore(ROW(1,2))</code> → <code class="returnvalue">"f1"=&gt;"1", "f2"=&gt;"2"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="function">hstore</code> ( <code class="type">text[]</code> ) → <code class="returnvalue">hstore</code></p>
<p>Constructs an <code class="type">hstore</code> from an array, which may be either a key/value array, or a two-dimensional array.</p>
<p><code class="literal">hstore(ARRAY['a','1','b','2'])</code> → <code class="returnvalue">"a"=&gt;"1", "b"=&gt;"2"</code></p>
<p><code class="literal">hstore(ARRAY[['c','3'],['d','4']])</code> → <code class="returnvalue">"c"=&gt;"3", "d"=&gt;"4"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="function">hstore</code> ( <code class="type">text[]</code>, <code class="type">text[]</code> ) → <code class="returnvalue">hstore</code></p>
<p>Constructs an <code class="type">hstore</code> from separate key and value arrays.</p>
<p><code class="literal">hstore(ARRAY['a','b'], ARRAY['1','2'])</code> → <code class="returnvalue">"a"=&gt;"1", "b"=&gt;"2"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="function">hstore</code> ( <code class="type">text</code>, <code class="type">text</code> ) → <code class="returnvalue">hstore</code></p>
<p>Makes a single-item <code class="type">hstore</code>.</p>
<p><code class="literal">hstore('a', 'b')</code> → <code class="returnvalue">"a"=&gt;"b"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.5.1.1.1" name="id-1.11.7.27.6.4.2.2.5.1.1.1"></a> <code class="function">akeys</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">text[]</code></p>
<p>Extracts an <code class="type">hstore</code>'s keys as an array.</p>
<p><code class="literal">akeys('a=&gt;1,b=&gt;2')</code> → <code class="returnvalue">{a,b}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.6.1.1.1" name="id-1.11.7.27.6.4.2.2.6.1.1.1"></a> <code class="function">skeys</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">setof text</code></p>
<p>Extracts an <code class="type">hstore</code>'s keys as a set.</p>
<p><code class="literal">skeys('a=&gt;1,b=&gt;2')</code> →</p>
<pre class="programlisting">a
b
</pre>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.7.1.1.1" name="id-1.11.7.27.6.4.2.2.7.1.1.1"></a> <code class="function">avals</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">text[]</code></p>
<p>Extracts an <code class="type">hstore</code>'s values as an array.</p>
<p><code class="literal">avals('a=&gt;1,b=&gt;2')</code> → <code class="returnvalue">{1,2}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.8.1.1.1" name="id-1.11.7.27.6.4.2.2.8.1.1.1"></a> <code class="function">svals</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">setof text</code></p>
<p>Extracts an <code class="type">hstore</code>'s values as a set.</p>
<p><code class="literal">svals('a=&gt;1,b=&gt;2')</code> →</p>
<pre class="programlisting">1
2
</pre>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.9.1.1.1" name="id-1.11.7.27.6.4.2.2.9.1.1.1"></a> <code class="function">hstore_to_array</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">text[]</code></p>
<p>Extracts an <code class="type">hstore</code>'s keys and values as an array of alternating keys and values.</p>
<p><code class="literal">hstore_to_array('a=&gt;1,b=&gt;2')</code> → <code class="returnvalue">{a,1,b,2}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.10.1.1.1" name="id-1.11.7.27.6.4.2.2.10.1.1.1"></a> <code class="function">hstore_to_matrix</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">text[]</code></p>
<p>Extracts an <code class="type">hstore</code>'s keys and values as a two-dimensional array.</p>
<p><code class="literal">hstore_to_matrix('a=&gt;1,b=&gt;2')</code> → <code class="returnvalue">{{a,1},{b,2}}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.11.1.1.1" name="id-1.11.7.27.6.4.2.2.11.1.1.1"></a> <code class="function">hstore_to_json</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">json</code></p>
<p>Converts an <code class="type">hstore</code> to a <code class="type">json</code> value, converting all non-null values to JSON strings.</p>
<p>This function is used implicitly when an <code class="type">hstore</code> value is cast to <code class="type">json</code>.</p>
<p><code class="literal">hstore_to_json('"a key"=&gt;1, b=&gt;t, c=&gt;null, d=&gt;12345, e=&gt;012345, f=&gt;1.234, g=&gt;2.345e+4')</code> → <code class="returnvalue">{"a key": "1", "b": "t", "c": null, "d": "12345", "e": "012345", "f": "1.234", "g": "2.345e+4"}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.12.1.1.1" name="id-1.11.7.27.6.4.2.2.12.1.1.1"></a> <code class="function">hstore_to_jsonb</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">jsonb</code></p>
<p>Converts an <code class="type">hstore</code> to a <code class="type">jsonb</code> value, converting all non-null values to JSON strings.</p>
<p>This function is used implicitly when an <code class="type">hstore</code> value is cast to <code class="type">jsonb</code>.</p>
<p><code class="literal">hstore_to_jsonb('"a key"=&gt;1, b=&gt;t, c=&gt;null, d=&gt;12345, e=&gt;012345, f=&gt;1.234, g=&gt;2.345e+4')</code> → <code class="returnvalue">{"a key": "1", "b": "t", "c": null, "d": "12345", "e": "012345", "f": "1.234", "g": "2.345e+4"}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.13.1.1.1" name="id-1.11.7.27.6.4.2.2.13.1.1.1"></a> <code class="function">hstore_to_json_loose</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">json</code></p>
<p>Converts an <code class="type">hstore</code> to a <code class="type">json</code> value, but attempts to distinguish numerical and Boolean values so they are unquoted in the JSON.</p>
<p><code class="literal">hstore_to_json_loose('"a key"=&gt;1, b=&gt;t, c=&gt;null, d=&gt;12345, e=&gt;012345, f=&gt;1.234, g=&gt;2.345e+4')</code> → <code class="returnvalue">{"a key": 1, "b": true, "c": null, "d": 12345, "e": "012345", "f": 1.234, "g": 2.345e+4}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.14.1.1.1" name="id-1.11.7.27.6.4.2.2.14.1.1.1"></a> <code class="function">hstore_to_jsonb_loose</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">jsonb</code></p>
<p>Converts an <code class="type">hstore</code> to a <code class="type">jsonb</code> value, but attempts to distinguish numerical and Boolean values so they are unquoted in the JSON.</p>
<p><code class="literal">hstore_to_jsonb_loose('"a key"=&gt;1, b=&gt;t, c=&gt;null, d=&gt;12345, e=&gt;012345, f=&gt;1.234, g=&gt;2.345e+4')</code> → <code class="returnvalue">{"a key": 1, "b": true, "c": null, "d": 12345, "e": "012345", "f": 1.234, "g": 2.345e+4}</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.15.1.1.1" name="id-1.11.7.27.6.4.2.2.15.1.1.1"></a> <code class="function">slice</code> ( <code class="type">hstore</code>, <code class="type">text[]</code> ) → <code class="returnvalue">hstore</code></p>
<p>Extracts a subset of an <code class="type">hstore</code> containing only the specified keys.</p>
<p><code class="literal">slice('a=&gt;1,b=&gt;2,c=&gt;3'::hstore, ARRAY['b','c','x'])</code> → <code class="returnvalue">"b"=&gt;"2", "c"=&gt;"3"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.16.1.1.1" name="id-1.11.7.27.6.4.2.2.16.1.1.1"></a> <code class="function">each</code> ( <code class="type">hstore</code> ) → <code class="returnvalue">setof record</code> ( <em class="parameter"><code>key</code></em> <code class="type">text</code>, <em class="parameter"><code>value</code></em> <code class="type">text</code> )</p>
<p>Extracts an <code class="type">hstore</code>'s keys and values as a set of records.</p>
<p><code class="literal">select * from each('a=&gt;1,b=&gt;2')</code> →</p>
<pre class="programlisting"> key | value
-----+-------
 a   | 1
 b   | 2
</pre>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.17.1.1.1" name="id-1.11.7.27.6.4.2.2.17.1.1.1"></a> <code class="function">exist</code> ( <code class="type">hstore</code>, <code class="type">text</code> ) → <code class="returnvalue">boolean</code></p>
<p>Does <code class="type">hstore</code> contain key?</p>
<p><code class="literal">exist('a=&gt;1', 'a')</code> → <code class="returnvalue">t</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.18.1.1.1" name="id-1.11.7.27.6.4.2.2.18.1.1.1"></a> <code class="function">defined</code> ( <code class="type">hstore</code>, <code class="type">text</code> ) → <code class="returnvalue">boolean</code></p>
<p>Does <code class="type">hstore</code> contain a non-<code class="literal">NULL</code> value for key?</p>
<p><code class="literal">defined('a=&gt;NULL', 'a')</code> → <code class="returnvalue">f</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.19.1.1.1" name="id-1.11.7.27.6.4.2.2.19.1.1.1"></a> <code class="function">delete</code> ( <code class="type">hstore</code>, <code class="type">text</code> ) → <code class="returnvalue">hstore</code></p>
<p>Deletes pair with matching key.</p>
<p><code class="literal">delete('a=&gt;1,b=&gt;2', 'b')</code> → <code class="returnvalue">"a"=&gt;"1"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="function">delete</code> ( <code class="type">hstore</code>, <code class="type">text[]</code> ) → <code class="returnvalue">hstore</code></p>
<p>Deletes pairs with matching keys.</p>
<p><code class="literal">delete('a=&gt;1,b=&gt;2,c=&gt;3', ARRAY['a','b'])</code> → <code class="returnvalue">"c"=&gt;"3"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><code class="function">delete</code> ( <code class="type">hstore</code>, <code class="type">hstore</code> ) → <code class="returnvalue">hstore</code></p>
<p>Deletes pairs matching those in the second argument.</p>
<p><code class="literal">delete('a=&gt;1,b=&gt;2', 'a=&gt;4,b=&gt;2'::hstore)</code> → <code class="returnvalue">"a"=&gt;"1"</code></p>
</td>
</tr>
<tr>
<td class="func_table_entry">
<p class="func_signature"><a class="indexterm" id="id-1.11.7.27.6.4.2.2.22.1.1.1" name="id-1.11.7.27.6.4.2.2.22.1.1.1"></a> <code class="function">populate_record</code> ( <code class="type">anyelement</code>, <code class="type">hstore</code> ) → <code class="returnvalue">anyelement</code></p>
<p>Replaces fields in the left operand (which must be a composite type) with matching values from <code class="type">hstore</code>.</p>
<p><code class="literal">populate_record(ROW(1,2), 'f1=&gt;42'::hstore)</code> → <code class="returnvalue">(42,2)</code></p>
</td>
</tr>
</tbody>
</table>
</div>
</div><br class="table-break"/>
<p>In addition to these operators and functions, values of the <code class="type">hstore</code> type can be subscripted, allowing them to act like associative arrays. Only a single subscript of type <code class="type">text</code> can be specified; it is interpreted as a key and the corresponding value is fetched or stored. For example,</p>
<pre class="programlisting">CREATE TABLE mytable (h hstore);
INSERT INTO mytable VALUES ('a=&gt;b, c=&gt;d');
SELECT h['a'] FROM mytable;
 h
---
 b
(1 row)

UPDATE mytable SET h['c'] = 'new';
SELECT h FROM mytable;
          h
----------------------
 "a"=&gt;"b", "c"=&gt;"new"
(1 row)
</pre>
<p>A subscripted fetch returns <code class="literal">NULL</code> if the subscript is <code class="literal">NULL</code> or that key does not exist in the <code class="type">hstore</code>. (Thus, a subscripted fetch is not greatly different from the <code class="literal">-&gt;</code> operator.) A subscripted update fails if the subscript is <code class="literal">NULL</code>; otherwise, it replaces the value for that key, adding an entry to the <code class="type">hstore</code> if the key does not already exist.</p>
</div>
<div class="sect2" id="HSTORE-INDEXES">
<div class="titlepage">
<div>
<div>
<h3 class="title">F.17.3. Indexes <a class="id_link" href="#HSTORE-INDEXES">#</a></h3>
</div>
</div>
</div>
<p><code class="type">hstore</code> has GiST and GIN index support for the <code class="literal">@&gt;</code>, <code class="literal">?</code>, <code class="literal">?&amp;</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="literal">gist_hstore_ops</code> GiST opclass approximates a set of key/value pairs as a bitmap signature. Its optional integer parameter <code class="literal">siglen</code> determines the signature length in bytes. The default length is 16 bytes. Valid values of signature length are between 1 and 2024 bytes. Longer signatures lead to a more precise search (scanning a smaller fraction of the index and fewer heap pages), at the cost of a larger index.</p>
<p>Example of creating such an index with a signature length of 32 bytes:</p>
<pre class="programlisting">CREATE INDEX hidx ON testhstore USING GIST (h gist_hstore_ops(siglen=32));
</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="HSTORE-EXAMPLES">
<div class="titlepage">
<div>
<div>
<h3 class="title">F.17.4. Examples <a class="id_link" href="#HSTORE-EXAMPLES">#</a></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['c'] = '3';
</pre>
<p>Another way to do the same thing is:</p>
<pre class="programlisting">UPDATE tab SET h = h || hstore('c', '3');
</pre>
<p>If multiple keys are to be added or changed in one operation, the concatenation approach is more efficient than subscripting:</p>
<pre class="programlisting">UPDATE tab SET h = h || hstore(array['q', 'w'], array['11', '12']);
</pre>
<p>Delete a key:</p>
<pre class="programlisting">UPDATE tab SET h = delete(h, 'k1');
</pre>
<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"=&gt;"123", "col2"=&gt;"foo", "col3"=&gt;"bar"
(1 row)
</pre>
<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"=&gt;"456", "col2"=&gt;"zzz"');
 col1 | col2 | col3
------+------+------
  456 | zzz  |
(1 row)
</pre>
<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"=&gt;"baz"' AS r FROM test t) s;
 col1 | col2 | col3
------+------+------
  123 | foo  | baz
(1 row)
</pre>
</div>
<div class="sect2" id="HSTORE-STATISTICS">
<div class="titlepage">
<div>
<div>
<h3 class="title">F.17.5. Statistics <a class="id_link" href="#HSTORE-STATISTICS">#</a></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=&gt;bq, b=&gt;NULL, ""=&gt;1');
</pre>
<p>Using a table:</p>
<pre class="programlisting">CREATE TABLE stat AS SELECT (each(h)).key, (each(h)).value FROM testhstore;
</pre>
<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>
</div>
<div class="sect2" id="HSTORE-COMPATIBILITY">
<div class="titlepage">
<div>
<div>
<h3 class="title">F.17.6. Compatibility <a class="id_link" href="#HSTORE-COMPATIBILITY">#</a></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>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 <code class="literal">ACCESS EXCLUSIVE</code> lock on the table, but does not result in bloating the table with old row versions.</p>
</div>
<div class="sect2" id="HSTORE-TRANSFORMS">
<div class="titlepage">
<div>
<div>
<h3 class="title">F.17.7. Transforms <a class="id_link" href="#HSTORE-TRANSFORMS">#</a></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 extension for PL/Python is called <code class="literal">hstore_plpython3u</code>. If you use it, <code class="type">hstore</code> values are mapped to Python dictionaries.</p>
</div>
<div class="sect2" id="HSTORE-AUTHORS">
<div class="titlepage">
<div>
<div>
<h3 class="title">F.17.8. Authors <a class="id_link" href="#HSTORE-AUTHORS">#</a></h3>
</div>
</div>
</div>
<p>Oleg Bartunov <code class="email">&lt;<a class="email" href="mailto:oleg@sai.msu.su">oleg@sai.msu.su</a>&gt;</code>, Moscow, Moscow University, Russia</p>
<p>Teodor Sigaev <code class="email">&lt;<a class="email" href="mailto:teodor@sigaev.ru">teodor@sigaev.ru</a>&gt;</code>, Moscow, Delta-Soft Ltd., Russia</p>
<p>Additional enhancements by Andrew Gierth <code class="email">&lt;<a class="email" href="mailto:andrew@tao11.riddles.org.uk">andrew@tao11.riddles.org.uk</a>&gt;</code>, United Kingdom</p>
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