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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!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.18. hstore — hstore key/value datatype</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 Vsnapshot" /><link rel="prev" href="fuzzystrmatch.html" title="F.17. fuzzystrmatch — determine string similarities and distance" /><link rel="next" href="intagg.html" title="F.19. intagg — integer aggregator and enumerator" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.18. hstore — hstore key/value datatype</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="fuzzystrmatch.html" title="F.17. fuzzystrmatch — determine string similarities and distance">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="intagg.html" title="F.19. intagg — integer aggregator and enumerator">Next</a></td></tr></table><hr /></div><div class="sect1" id="HSTORE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.18. hstore — hstore key/value datatype <a href="#HSTORE" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="hstore.html#HSTORE-EXTERNAL-REP">F.18.1. <code class="type">hstore</code> External Representation</a></span></dt><dt><span class="sect2"><a href="hstore.html#HSTORE-OPS-FUNCS">F.18.2. <code class="type">hstore</code> Operators and Functions</a></span></dt><dt><span class="sect2"><a href="hstore.html#HSTORE-INDEXES">F.18.3. Indexes</a></span></dt><dt><span class="sect2"><a href="hstore.html#HSTORE-EXAMPLES">F.18.4. Examples</a></span></dt><dt><span class="sect2"><a href="hstore.html#HSTORE-STATISTICS">F.18.5. Statistics</a></span></dt><dt><span class="sect2"><a href="hstore.html#HSTORE-COMPATIBILITY">F.18.6. Compatibility</a></span></dt><dt><span class="sect2"><a href="hstore.html#HSTORE-TRANSFORMS">F.18.7. Transforms</a></span></dt><dt><span class="sect2"><a href="hstore.html#HSTORE-AUTHORS">F.18.8. Authors</a></span></dt></dl></div><a id="id-1.11.7.28.2" 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><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.18.1. <code class="type">hstore</code> External Representation <a href="#HSTORE-EXTERNAL-REP" class="id_link">#</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">=></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="HSTORE-OPS-FUNCS"><div class="titlepage"><div><div><h3 class="title">F.18.2. <code class="type">hstore</code> Operators and Functions <a href="#HSTORE-OPS-FUNCS" class="id_link">#</a></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 /></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">-></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=>x, b=>y'::hstore -> '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">-></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=>x, b=>y, c=>z'::hstore -> 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=>b, c=>d'::hstore || 'c=>x, d=>q'::hstore</code>
→ <code class="returnvalue">"a"=>"b", "c"=>"x", "d"=>"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=>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">?&</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=>1,b=>2'::hstore ?& 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=>1,b=>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">@></code> <code class="type">hstore</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does left operand contain right?
</p>
<p>
<code class="literal">'a=>b, b=>1, c=>NULL'::hstore @> 'b=>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"><@</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=>c'::hstore <@ 'a=>b, b=>1, c=>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=>1, b=>2, c=>3'::hstore - 'b'::text</code>
→ <code class="returnvalue">"a"=>"1", "c"=>"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=>1, b=>2, c=>3'::hstore - ARRAY['a','b']</code>
→ <code class="returnvalue">"c"=>"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=>1, b=>2, c=>3'::hstore - 'a=>4, b=>2'::hstore</code>
→ <code class="returnvalue">"a"=>"1", "c"=>"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=>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=>foo, b=>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=>foo, b=>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.8. <code class="type">hstore</code> Functions</strong></p><div class="table-contents"><table class="table" summary="hstore Functions" border="1"><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 id="id-1.11.7.28.6.4.2.2.1.1.1.1" class="indexterm"></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"=>"1", "f2"=>"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"=>"1", "b"=>"2"</code>
</p>
<p>
<code class="literal">hstore(ARRAY[['c','3'],['d','4']])</code>
→ <code class="returnvalue">"c"=>"3", "d"=>"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"=>"1", "b"=>"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"=>"b"</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.5.1.1.1" class="indexterm"></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=>1,b=>2')</code>
→ <code class="returnvalue">{a,b}</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.6.1.1.1" class="indexterm"></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=>1,b=>2')</code>
→ <code class="returnvalue"></code>
</p><pre class="programlisting">
a
b
</pre><p>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.7.1.1.1" class="indexterm"></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=>1,b=>2')</code>
→ <code class="returnvalue">{1,2}</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.8.1.1.1" class="indexterm"></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=>1,b=>2')</code>
→ <code class="returnvalue"></code>
</p><pre class="programlisting">
1
2
</pre><p>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.9.1.1.1" class="indexterm"></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=>1,b=>2')</code>
→ <code class="returnvalue">{a,1,b,2}</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.10.1.1.1" class="indexterm"></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=>1,b=>2')</code>
→ <code class="returnvalue">{{a,1},{b,2}}</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.11.1.1.1" class="indexterm"></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"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>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 id="id-1.11.7.28.6.4.2.2.12.1.1.1" class="indexterm"></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"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>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 id="id-1.11.7.28.6.4.2.2.13.1.1.1" class="indexterm"></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"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>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 id="id-1.11.7.28.6.4.2.2.14.1.1.1" class="indexterm"></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"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>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 id="id-1.11.7.28.6.4.2.2.15.1.1.1" class="indexterm"></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=>1,b=>2,c=>3'::hstore, ARRAY['b','c','x'])</code>
→ <code class="returnvalue">"b"=>"2", "c"=>"3"</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.16.1.1.1" class="indexterm"></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=>1,b=>2')</code>
→ <code class="returnvalue"></code>
</p><pre class="programlisting">
key | value
-----+-------
a | 1
b | 2
</pre><p>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.17.1.1.1" class="indexterm"></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=>1', 'a')</code>
→ <code class="returnvalue">t</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.18.1.1.1" class="indexterm"></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=>NULL', 'a')</code>
→ <code class="returnvalue">f</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.19.1.1.1" class="indexterm"></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=>1,b=>2', 'b')</code>
→ <code class="returnvalue">"a"=>"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=>1,b=>2,c=>3', ARRAY['a','b'])</code>
→ <code class="returnvalue">"c"=>"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=>1,b=>2', 'a=>4,b=>2'::hstore)</code>
→ <code class="returnvalue">"a"=>"1"</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.28.6.4.2.2.22.1.1.1" class="indexterm"></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=>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=>b, c=>d');
SELECT h['a'] FROM mytable;
h
---
b
(1 row)
UPDATE mytable SET h['c'] = 'new';
SELECT h FROM mytable;
h
----------------------
"a"=>"b", "c"=>"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">-></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.18.3. Indexes <a href="#HSTORE-INDEXES" class="id_link">#</a></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="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>
</p><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.18.4. Examples <a href="#HSTORE-EXAMPLES" class="id_link">#</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>
</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="HSTORE-STATISTICS"><div class="titlepage"><div><div><h3 class="title">F.18.5. Statistics <a href="#HSTORE-STATISTICS" class="id_link">#</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=>bq, b=>NULL, ""=>1');
</pre><p>
</p><p>
Using a table:
</p><pre class="programlisting">
CREATE TABLE stat AS SELECT (each(h)).key, (each(h)).value 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="HSTORE-COMPATIBILITY"><div class="titlepage"><div><div><h3 class="title">F.18.6. Compatibility <a href="#HSTORE-COMPATIBILITY" class="id_link">#</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>
</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
<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.18.7. Transforms <a href="#HSTORE-TRANSFORMS" class="id_link">#</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 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="HSTORE-AUTHORS"><div class="titlepage"><div><div><h3 class="title">F.18.8. Authors <a href="#HSTORE-AUTHORS" class="id_link">#</a></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" title="F.17. fuzzystrmatch — determine string similarities and distance">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="intagg.html" title="F.19. intagg — integer aggregator and enumerator">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.17. fuzzystrmatch — determine string similarities and distance </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.19. intagg — integer aggregator and enumerator</td></tr></table></div></body></html>
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