636 lines
21 KiB
Plaintext
636 lines
21 KiB
Plaintext
<!-- doc/src/sgml/hstore.sgml -->
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<sect1 id="hstore" xreflabel="hstore">
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<title>hstore</title>
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<indexterm zone="hstore">
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<primary>hstore</primary>
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</indexterm>
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<para>
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This module implements the <type>hstore</> data type for storing sets of
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key/value pairs within a single <productname>PostgreSQL</> value.
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This can be useful in various scenarios, such as rows with many attributes
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that are rarely examined, or semi-structured data. Keys and values are
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simply text strings.
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</para>
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<sect2>
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<title><type>hstore</> External Representation</title>
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<para>
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The text representation of an <type>hstore</>, used for input and output,
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includes zero or more <replaceable>key</> <literal>=></>
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<replaceable>value</> pairs separated by commas. Some examples:
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<synopsis>
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k => v
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foo => bar, baz => whatever
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"1-a" => "anything at all"
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</synopsis>
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The order of the pairs is not significant (and may not be reproduced on
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output). Whitespace between pairs or around the <literal>=></> sign is
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ignored. Double-quote keys and values that include whitespace, commas,
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<literal>=</>s or <literal>></>s. To include a double quote or a
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backslash in a key or value, escape it with a backslash.
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</para>
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<para>
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Each key in an <type>hstore</> is unique. If you declare an <type>hstore</>
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with duplicate keys, only one will be stored in the <type>hstore</> and
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there is no guarantee as to which will be kept:
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<programlisting>
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SELECT 'a=>1,a=>2'::hstore;
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hstore
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----------
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"a"=>"1"
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</programlisting>
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</para>
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<para>
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A value (but not a key) can be an SQL <literal>NULL</>. For example:
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<programlisting>
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key => NULL
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</programlisting>
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The <literal>NULL</> keyword is case-insensitive. Double-quote the
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<literal>NULL</> to treat it as the ordinary string <quote>NULL</quote>.
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</para>
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<note>
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<para>
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Keep in mind that the <type>hstore</> text format, when used for input,
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applies <emphasis>before</> any required quoting or escaping. If you are
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passing an <type>hstore</> literal via a parameter, then no additional
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processing is needed. But if you're passing it as a quoted literal
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constant, then any single-quote characters and (depending on the setting of
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the <varname>standard_conforming_strings</> configuration parameter)
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backslash characters need to be escaped correctly. See
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<xref linkend="sql-syntax-strings"> for more on the handling of string
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constants.
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</para>
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</note>
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<para>
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On output, double quotes always surround keys and values, even when it's
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not strictly necessary.
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</para>
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</sect2>
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<sect2>
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<title><type>hstore</> Operators and Functions</title>
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<para>
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The operators provided by the <literal>hstore</literal> module are
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shown in <xref linkend="hstore-op-table">, the functions
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in <xref linkend="hstore-func-table">.
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</para>
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<table id="hstore-op-table">
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<title><type>hstore</> Operators</title>
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<tgroup cols="4">
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<thead>
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<row>
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<entry>Operator</entry>
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<entry>Description</entry>
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<entry>Example</entry>
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<entry>Result</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><type>hstore</> <literal>-></> <type>text</></entry>
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<entry>get value for key (<literal>NULL</> if not present)</entry>
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<entry><literal>'a=>x, b=>y'::hstore -> 'a'</literal></entry>
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<entry><literal>x</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>-></> <type>text[]</></entry>
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<entry>get values for keys (<literal>NULL</> if not present)</entry>
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<entry><literal>'a=>x, b=>y, c=>z'::hstore -> ARRAY['c','a']</literal></entry>
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<entry><literal>{"z","x"}</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>||</> <type>hstore</></entry>
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<entry>concatenate <type>hstore</>s</entry>
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<entry><literal>'a=>b, c=>d'::hstore || 'c=>x, d=>q'::hstore</literal></entry>
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<entry><literal>"a"=>"b", "c"=>"x", "d"=>"q"</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>?</> <type>text</></entry>
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<entry>does <type>hstore</> contain key?</entry>
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<entry><literal>'a=>1'::hstore ? 'a'</literal></entry>
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<entry><literal>t</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>?&</> <type>text[]</></entry>
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<entry>does <type>hstore</> contain all specified keys?</entry>
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<entry><literal>'a=>1,b=>2'::hstore ?& ARRAY['a','b']</literal></entry>
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<entry><literal>t</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>?|</> <type>text[]</></entry>
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<entry>does <type>hstore</> contain any of the specified keys?</entry>
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<entry><literal>'a=>1,b=>2'::hstore ?| ARRAY['b','c']</literal></entry>
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<entry><literal>t</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>@></> <type>hstore</></entry>
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<entry>does left operand contain right?</entry>
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<entry><literal>'a=>b, b=>1, c=>NULL'::hstore @> 'b=>1'</literal></entry>
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<entry><literal>t</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal><@</> <type>hstore</></entry>
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<entry>is left operand contained in right?</entry>
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<entry><literal>'a=>c'::hstore <@ 'a=>b, b=>1, c=>NULL'</literal></entry>
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<entry><literal>f</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>-</> <type>text</></entry>
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<entry>delete key from left operand</entry>
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<entry><literal>'a=>1, b=>2, c=>3'::hstore - 'b'::text</literal></entry>
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<entry><literal>"a"=>"1", "c"=>"3"</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>-</> <type>text[]</></entry>
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<entry>delete keys from left operand</entry>
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<entry><literal>'a=>1, b=>2, c=>3'::hstore - ARRAY['a','b']</literal></entry>
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<entry><literal>"c"=>"3"</literal></entry>
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</row>
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<row>
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<entry><type>hstore</> <literal>-</> <type>hstore</></entry>
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<entry>delete matching pairs from left operand</entry>
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<entry><literal>'a=>1, b=>2, c=>3'::hstore - 'a=>4, b=>2'::hstore</literal></entry>
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<entry><literal>"a"=>"1", "c"=>"3"</literal></entry>
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</row>
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<row>
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<entry><type>record</> <literal>#=</> <type>hstore</></entry>
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<entry>replace fields in <type>record</> with matching values from <type>hstore</></entry>
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<entry>see Examples section</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>%%</> <type>hstore</></entry>
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<entry>convert <type>hstore</> to array of alternating keys and values</entry>
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<entry><literal>%% 'a=>foo, b=>bar'::hstore</literal></entry>
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<entry><literal>{a,foo,b,bar}</literal></entry>
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</row>
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<row>
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<entry><literal>%#</> <type>hstore</></entry>
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<entry>convert <type>hstore</> to two-dimensional key/value array</entry>
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<entry><literal>%# 'a=>foo, b=>bar'::hstore</literal></entry>
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<entry><literal>{{a,foo},{b,bar}}</literal></entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<note>
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<para>
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Prior to PostgreSQL 8.2, the containment operators <literal>@></>
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and <literal><@</> were called <literal>@</> and <literal>~</>,
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respectively. These names are still available, but are deprecated and will
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eventually be removed. Notice that the old names are reversed from the
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convention formerly followed by the core geometric data types!
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</para>
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</note>
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<table id="hstore-func-table">
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<title><type>hstore</> Functions</title>
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<tgroup cols="5">
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<thead>
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<row>
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<entry>Function</entry>
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<entry>Return Type</entry>
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<entry>Description</entry>
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<entry>Example</entry>
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<entry>Result</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><function>hstore(record)</function><indexterm><primary>hstore</primary></indexterm></entry>
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<entry><type>hstore</type></entry>
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<entry>construct an <type>hstore</> from a record or row</entry>
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<entry><literal>hstore(ROW(1,2))</literal></entry>
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<entry><literal>f1=>1,f2=>2</literal></entry>
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</row>
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<row>
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<entry><function>hstore(text[])</function></entry>
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<entry><type>hstore</type></entry>
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<entry>construct an <type>hstore</> from an array, which may be either
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a key/value array, or a two-dimensional array</entry>
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<entry><literal>hstore(ARRAY['a','1','b','2']) || hstore(ARRAY[['c','3'],['d','4']])</literal></entry>
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<entry><literal>a=>1, b=>2, c=>3, d=>4</literal></entry>
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</row>
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<row>
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<entry><function>hstore(text[], text[])</function></entry>
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<entry><type>hstore</type></entry>
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<entry>construct an <type>hstore</> from separate key and value arrays</entry>
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<entry><literal>hstore(ARRAY['a','b'], ARRAY['1','2'])</literal></entry>
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<entry><literal>"a"=>"1","b"=>"2"</literal></entry>
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</row>
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<row>
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<entry><function>hstore(text, text)</function></entry>
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<entry><type>hstore</type></entry>
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<entry>make single-item <type>hstore</></entry>
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<entry><literal>hstore('a', 'b')</literal></entry>
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<entry><literal>"a"=>"b"</literal></entry>
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</row>
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<row>
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<entry><function>akeys(hstore)</function><indexterm><primary>akeys</primary></indexterm></entry>
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<entry><type>text[]</type></entry>
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<entry>get <type>hstore</>'s keys as an array</entry>
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<entry><literal>akeys('a=>1,b=>2')</literal></entry>
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<entry><literal>{a,b}</literal></entry>
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</row>
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<row>
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<entry><function>skeys(hstore)</function><indexterm><primary>skeys</primary></indexterm></entry>
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<entry><type>setof text</type></entry>
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<entry>get <type>hstore</>'s keys as a set</entry>
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<entry><literal>skeys('a=>1,b=>2')</literal></entry>
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<entry>
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<programlisting>
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a
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b
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</programlisting></entry>
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</row>
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<row>
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<entry><function>avals(hstore)</function><indexterm><primary>avals</primary></indexterm></entry>
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<entry><type>text[]</type></entry>
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<entry>get <type>hstore</>'s values as an array</entry>
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<entry><literal>avals('a=>1,b=>2')</literal></entry>
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<entry><literal>{1,2}</literal></entry>
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</row>
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<row>
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<entry><function>svals(hstore)</function><indexterm><primary>svals</primary></indexterm></entry>
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<entry><type>setof text</type></entry>
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<entry>get <type>hstore</>'s values as a set</entry>
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<entry><literal>svals('a=>1,b=>2')</literal></entry>
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<entry>
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<programlisting>
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1
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2
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</programlisting></entry>
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</row>
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<row>
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<entry><function>hstore_to_array(hstore)</function><indexterm><primary>hstore_to_array</primary></indexterm></entry>
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<entry><type>text[]</type></entry>
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<entry>get <type>hstore</>'s keys and values as an array of alternating
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keys and values</entry>
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<entry><literal>hstore_to_array('a=>1,b=>2')</literal></entry>
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<entry><literal>{a,1,b,2}</literal></entry>
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</row>
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<row>
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<entry><function>hstore_to_matrix(hstore)</function><indexterm><primary>hstore_to_matrix</primary></indexterm></entry>
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<entry><type>text[]</type></entry>
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<entry>get <type>hstore</>'s keys and values as a two-dimensional array</entry>
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<entry><literal>hstore_to_matrix('a=>1,b=>2')</literal></entry>
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<entry><literal>{{a,1},{b,2}}</literal></entry>
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</row>
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<row>
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<entry><function>hstore_to_json(hstore)</function><indexterm><primary>hstore_to_json</primary></indexterm></entry>
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<entry><type>json</type></entry>
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<entry>get <type>hstore</type> as a <type>json</type> value</entry>
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<entry><literal>hstore_to_json('"a key"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>2.345e+4')</literal></entry>
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<entry><literal>{"a key": "1", "b": "t", "c": null, "d": "12345", "e": "012345", "f": "1.234", "g": "2.345e+4"}</literal></entry>
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</row>
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<row>
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<entry><function>hstore_to_json_loose(hstore)</function><indexterm><primary>hstore_to_json_loose</primary></indexterm></entry>
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<entry><type>json</type></entry>
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<entry>get <type>hstore</type> as a <type>json</type> value, but attempt to distinguish numerical and Boolean values so they are unquoted in the JSON</entry>
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<entry><literal>hstore_to_json_loose('"a key"=>1, b=>t, c=>null, d=>12345, e=>012345, f=>1.234, g=>2.345e+4')</literal></entry>
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<entry><literal>{"a key": 1, "b": true, "c": null, "d": 12345, "e": "012345", "f": 1.234, "g": 2.345e+4}</literal></entry>
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</row>
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<row>
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<entry><function>slice(hstore, text[])</function><indexterm><primary>slice</primary></indexterm></entry>
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<entry><type>hstore</type></entry>
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<entry>extract a subset of an <type>hstore</></entry>
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<entry><literal>slice('a=>1,b=>2,c=>3'::hstore, ARRAY['b','c','x'])</literal></entry>
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<entry><literal>"b"=>"2", "c"=>"3"</literal></entry>
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</row>
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<row>
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<entry><function>each(hstore)</function><indexterm><primary>each</primary></indexterm></entry>
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<entry><type>setof(key text, value text)</type></entry>
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<entry>get <type>hstore</>'s keys and values as a set</entry>
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<entry><literal>select * from each('a=>1,b=>2')</literal></entry>
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<entry>
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<programlisting>
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key | value
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-----+-------
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a | 1
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b | 2
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</programlisting></entry>
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</row>
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<row>
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<entry><function>exist(hstore,text)</function><indexterm><primary>exist</primary></indexterm></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>hstore</> contain key?</entry>
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<entry><literal>exist('a=>1','a')</literal></entry>
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<entry><literal>t</literal></entry>
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</row>
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<row>
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<entry><function>defined(hstore,text)</function><indexterm><primary>defined</primary></indexterm></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>hstore</> contain non-<literal>NULL</> value for key?</entry>
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<entry><literal>defined('a=>NULL','a')</literal></entry>
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<entry><literal>f</literal></entry>
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</row>
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<row>
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<entry><function>delete(hstore,text)</function><indexterm><primary>delete</primary></indexterm></entry>
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<entry><type>hstore</type></entry>
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<entry>delete pair with matching key</entry>
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<entry><literal>delete('a=>1,b=>2','b')</literal></entry>
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<entry><literal>"a"=>"1"</literal></entry>
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</row>
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<row>
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<entry><function>delete(hstore,text[])</function></entry>
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<entry><type>hstore</type></entry>
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<entry>delete pairs with matching keys</entry>
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<entry><literal>delete('a=>1,b=>2,c=>3',ARRAY['a','b'])</literal></entry>
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<entry><literal>"c"=>"3"</literal></entry>
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</row>
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<row>
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<entry><function>delete(hstore,hstore)</function></entry>
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<entry><type>hstore</type></entry>
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<entry>delete pairs matching those in the second argument</entry>
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<entry><literal>delete('a=>1,b=>2','a=>4,b=>2'::hstore)</literal></entry>
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<entry><literal>"a"=>"1"</literal></entry>
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</row>
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<row>
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<entry><function>populate_record(record,hstore)</function><indexterm><primary>populate_record</primary></indexterm></entry>
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<entry><type>record</type></entry>
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<entry>replace fields in <type>record</> with matching values from <type>hstore</></entry>
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<entry>see Examples section</entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<note>
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<para>
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The function <function>hstore_to_json</function> is used when an <type>hstore</type>
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value is cast to <type>json</type>.
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</para>
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</note>
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<note>
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<para>
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The function <function>populate_record</function> is actually declared
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with <type>anyelement</>, not <type>record</>, as its first argument,
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but it will reject non-record types with a run-time error.
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</para>
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</note>
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</sect2>
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<sect2>
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<title>Indexes</title>
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<para>
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<type>hstore</> has GiST and GIN index support for the <literal>@></>,
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<literal>?</>, <literal>?&</> and <literal>?|</> operators. For example:
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</para>
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<programlisting>
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CREATE INDEX hidx ON testhstore USING GIST (h);
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CREATE INDEX hidx ON testhstore USING GIN (h);
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</programlisting>
|
|
|
|
<para>
|
|
<type>hstore</> also supports <type>btree</> or <type>hash</> indexes for
|
|
the <literal>=</> operator. This allows <type>hstore</> columns to be
|
|
declared <literal>UNIQUE</>, or to be used in <literal>GROUP BY</>,
|
|
<literal>ORDER BY</> or <literal>DISTINCT</> expressions. The sort ordering
|
|
for <type>hstore</> values is not particularly useful, but these indexes
|
|
may be useful for equivalence lookups. Create indexes for <literal>=</>
|
|
comparisons as follows:
|
|
</para>
|
|
<programlisting>
|
|
CREATE INDEX hidx ON testhstore USING BTREE (h);
|
|
|
|
CREATE INDEX hidx ON testhstore USING HASH (h);
|
|
</programlisting>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Examples</title>
|
|
|
|
<para>
|
|
Add a key, or update an existing key with a new value:
|
|
<programlisting>
|
|
UPDATE tab SET h = h || hstore('c', '3');
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Delete a key:
|
|
<programlisting>
|
|
UPDATE tab SET h = delete(h, 'k1');
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Convert a <type>record</> to an <type>hstore</>:
|
|
<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)
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Convert an <type>hstore</> to a predefined <type>record</> type:
|
|
<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)
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Modify an existing record using the values from an <type>hstore</>:
|
|
<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)
|
|
</programlisting>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Statistics</title>
|
|
|
|
<para>
|
|
The <type>hstore</> 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.
|
|
</para>
|
|
|
|
<para>
|
|
Simple example:
|
|
<programlisting>
|
|
SELECT * FROM each('aaa=>bq, b=>NULL, ""=>1');
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Using a table:
|
|
<programlisting>
|
|
SELECT (each(h)).key, (each(h)).value INTO stat FROM testhstore;
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Online statistics:
|
|
<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
|
|
...................
|
|
</programlisting>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Compatibility</title>
|
|
|
|
<para>
|
|
As of PostgreSQL 9.0, <type>hstore</> 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.
|
|
</para>
|
|
|
|
<para>
|
|
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 <literal>UPDATE</> statement as follows:
|
|
<programlisting>
|
|
UPDATE tablename SET hstorecol = hstorecol || '';
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Another way to do it is:
|
|
<programlisting>
|
|
ALTER TABLE tablename ALTER hstorecol TYPE hstore USING hstorecol || '';
|
|
</programlisting>
|
|
The <command>ALTER TABLE</> method requires an exclusive lock on the table,
|
|
but does not result in bloating the table with old row versions.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Transforms</title>
|
|
|
|
<para>
|
|
Additional extensions are available that implement transforms for
|
|
the <type>hstore</type> type for the languages PL/Perl and PL/Python. The
|
|
extensions for PL/Perl are called <literal>hstore_plperl</literal>
|
|
and <literal>hstore_plperlu</literal>, for trusted and untrusted PL/Perl.
|
|
If you install these transforms and specify them when creating a
|
|
function, <type>hstore</type> values are mapped to Perl hashes. The
|
|
extensions for PL/Python are
|
|
called <literal>hstore_plpythonu</literal>, <literal>hstore_plpython2u</literal>,
|
|
and <literal>hstore_plpython3u</literal>
|
|
(see <xref linkend="plpython-python23"> for the PL/Python naming
|
|
convention). If you use them, <type>hstore</type> values are mapped to
|
|
Python dictionaries.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Authors</title>
|
|
|
|
<para>
|
|
Oleg Bartunov <email>oleg@sai.msu.su</email>, Moscow, Moscow University, Russia
|
|
</para>
|
|
|
|
<para>
|
|
Teodor Sigaev <email>teodor@sigaev.ru</email>, Moscow, Delta-Soft Ltd., Russia
|
|
</para>
|
|
|
|
<para>
|
|
Additional enhancements by Andrew Gierth <email>andrew@tao11.riddles.org.uk</email>,
|
|
United Kingdom
|
|
</para>
|
|
</sect2>
|
|
|
|
</sect1>
|