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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >hstore</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Additional Supplied Modules" HREF="contrib.html"><LINK REL="PREVIOUS" TITLE="fuzzystrmatch" HREF="fuzzystrmatch.html"><LINK REL="NEXT" TITLE="intagg" HREF="intagg.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-11-06T22:43:11"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="fuzzystrmatch" HREF="fuzzystrmatch.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="contrib.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Appendix F. Additional Supplied Modules</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="intagg" HREF="intagg.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="HSTORE" >F.16. hstore</A ></H1 ><P > This module implements the <TT CLASS="TYPE" >hstore</TT > data type for storing sets of key/value pairs within a single <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > value. This can be useful in various scenarios, such as rows with many attributes that are rarely examined, or semi-structured data. Keys and values are simply text strings. </P ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN148339" >F.16.1. <TT CLASS="TYPE" >hstore</TT > External Representation</A ></H2 ><P > The text representation of an <TT CLASS="TYPE" >hstore</TT >, used for input and output, includes zero or more <TT CLASS="REPLACEABLE" ><I >key</I ></TT > <TT CLASS="LITERAL" >=></TT > <TT CLASS="REPLACEABLE" ><I >value</I ></TT > 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 <TT CLASS="LITERAL" >=></TT > sign is ignored. Double-quote keys and values that include whitespace, commas, <TT CLASS="LITERAL" >=</TT >s or <TT CLASS="LITERAL" >></TT >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 <TT CLASS="TYPE" >hstore</TT > is unique. If you declare an <TT CLASS="TYPE" >hstore</TT > with duplicate keys, only one will be stored in the <TT CLASS="TYPE" >hstore</TT > 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 <TT CLASS="LITERAL" >NULL</TT >. For example: </P><PRE CLASS="PROGRAMLISTING" >key => NULL</PRE ><P> The <TT CLASS="LITERAL" >NULL</TT > keyword is case-insensitive. Double-quote the <TT CLASS="LITERAL" >NULL</TT > to treat it as the ordinary string <SPAN CLASS="QUOTE" >"NULL"</SPAN >. </P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > Keep in mind that the <TT CLASS="TYPE" >hstore</TT > text format, when used for input, applies <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >before</I ></SPAN > any required quoting or escaping. If you are passing an <TT CLASS="TYPE" >hstore</TT > 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 <TT CLASS="VARNAME" >standard_conforming_strings</TT > configuration parameter) backslash characters need to be escaped correctly. See <A HREF="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS" >Section 4.1.2.1</A > for more on the handling of string constants. </P ></BLOCKQUOTE ></DIV ><P > On output, double quotes always surround keys and values, even when it's not strictly necessary. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN148370" >F.16.2. <TT CLASS="TYPE" >hstore</TT > Operators and Functions</A ></H2 ><P > The operators provided by the <TT CLASS="LITERAL" >hstore</TT > module are shown in <A HREF="hstore.html#HSTORE-OP-TABLE" >Table F-8</A >, the functions in <A HREF="hstore.html#HSTORE-FUNC-TABLE" >Table F-9</A >. </P ><DIV CLASS="TABLE" ><A NAME="HSTORE-OP-TABLE" ></A ><P ><B >Table F-8. <TT CLASS="TYPE" >hstore</TT > Operators</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><COL><THEAD ><TR ><TH >Operator</TH ><TH >Description</TH ><TH >Example</TH ><TH >Result</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >-></TT > <TT CLASS="TYPE" >text</TT ></TD ><TD >get value for key (<TT CLASS="LITERAL" >NULL</TT > if not present)</TD ><TD ><TT CLASS="LITERAL" >'a=>x, b=>y'::hstore -> 'a'</TT ></TD ><TD ><TT CLASS="LITERAL" >x</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >-></TT > <TT CLASS="TYPE" >text[]</TT ></TD ><TD >get values for keys (<TT CLASS="LITERAL" >NULL</TT > if not present)</TD ><TD ><TT CLASS="LITERAL" >'a=>x, b=>y, c=>z'::hstore -> ARRAY['c','a']</TT ></TD ><TD ><TT CLASS="LITERAL" >{"z","x"}</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >||</TT > <TT CLASS="TYPE" >hstore</TT ></TD ><TD >concatenate <TT CLASS="TYPE" >hstore</TT >s</TD ><TD ><TT CLASS="LITERAL" >'a=>b, c=>d'::hstore || 'c=>x, d=>q'::hstore</TT ></TD ><TD ><TT CLASS="LITERAL" >"a"=>"b", "c"=>"x", "d"=>"q"</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >?</TT > <TT CLASS="TYPE" >text</TT ></TD ><TD >does <TT CLASS="TYPE" >hstore</TT > contain key?</TD ><TD ><TT CLASS="LITERAL" >'a=>1'::hstore ? 'a'</TT ></TD ><TD ><TT CLASS="LITERAL" >t</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >?&</TT > <TT CLASS="TYPE" >text[]</TT ></TD ><TD >does <TT CLASS="TYPE" >hstore</TT > contain all specified keys?</TD ><TD ><TT CLASS="LITERAL" >'a=>1,b=>2'::hstore ?& ARRAY['a','b']</TT ></TD ><TD ><TT CLASS="LITERAL" >t</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >?|</TT > <TT CLASS="TYPE" >text[]</TT ></TD ><TD >does <TT CLASS="TYPE" >hstore</TT > contain any of the specified keys?</TD ><TD ><TT CLASS="LITERAL" >'a=>1,b=>2'::hstore ?| ARRAY['b','c']</TT ></TD ><TD ><TT CLASS="LITERAL" >t</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >@></TT > <TT CLASS="TYPE" >hstore</TT ></TD ><TD >does left operand contain right?</TD ><TD ><TT CLASS="LITERAL" >'a=>b, b=>1, c=>NULL'::hstore @> 'b=>1'</TT ></TD ><TD ><TT CLASS="LITERAL" >t</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" ><@</TT > <TT CLASS="TYPE" >hstore</TT ></TD ><TD >is left operand contained in right?</TD ><TD ><TT CLASS="LITERAL" >'a=>c'::hstore <@ 'a=>b, b=>1, c=>NULL'</TT ></TD ><TD ><TT CLASS="LITERAL" >f</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >-</TT > <TT CLASS="TYPE" >text</TT ></TD ><TD >delete key from left operand</TD ><TD ><TT CLASS="LITERAL" >'a=>1, b=>2, c=>3'::hstore - 'b'::text</TT ></TD ><TD ><TT CLASS="LITERAL" >"a"=>"1", "c"=>"3"</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >-</TT > <TT CLASS="TYPE" >text[]</TT ></TD ><TD >delete keys from left operand</TD ><TD ><TT CLASS="LITERAL" >'a=>1, b=>2, c=>3'::hstore - ARRAY['a','b']</TT ></TD ><TD ><TT CLASS="LITERAL" >"c"=>"3"</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >hstore</TT > <TT CLASS="LITERAL" >-</TT > <TT CLASS="TYPE" >hstore</TT ></TD ><TD >delete matching pairs from left operand</TD ><TD ><TT CLASS="LITERAL" >'a=>1, b=>2, c=>3'::hstore - 'a=>4, b=>2'::hstore</TT ></TD ><TD ><TT CLASS="LITERAL" >"a"=>"1", "c"=>"3"</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >record</TT > <TT CLASS="LITERAL" >#=</TT > <TT CLASS="TYPE" >hstore</TT ></TD ><TD >replace fields in <TT CLASS="TYPE" >record</TT > with matching values from <TT CLASS="TYPE" >hstore</TT ></TD ><TD >see Examples section</TD ><TD > </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >%%</TT > <TT CLASS="TYPE" >hstore</TT ></TD ><TD >convert <TT CLASS="TYPE" >hstore</TT > to array of alternating keys and values</TD ><TD ><TT CLASS="LITERAL" >%% 'a=>foo, b=>bar'::hstore</TT ></TD ><TD ><TT CLASS="LITERAL" >{a,foo,b,bar}</TT ></TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >%#</TT > <TT CLASS="TYPE" >hstore</TT ></TD ><TD >convert <TT CLASS="TYPE" >hstore</TT > to two-dimensional key/value array</TD ><TD ><TT CLASS="LITERAL" >%# 'a=>foo, b=>bar'::hstore</TT ></TD ><TD ><TT CLASS="LITERAL" >{{a,foo},{b,bar}}</TT ></TD ></TR ></TBODY ></TABLE ></DIV ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > Prior to PostgreSQL 8.2, the containment operators <TT CLASS="LITERAL" >@></TT > and <TT CLASS="LITERAL" ><@</TT > were called <TT CLASS="LITERAL" >@</TT > and <TT CLASS="LITERAL" >~</TT >, respectively. These names are still available, but are deprecated and will eventually be removed. Notice that the old names are reversed from the convention formerly followed by the core geometric data types! </P ></BLOCKQUOTE ></DIV ><DIV CLASS="TABLE" ><A NAME="HSTORE-FUNC-TABLE" ></A ><P ><B >Table F-9. <TT CLASS="TYPE" >hstore</TT > Functions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><COL><COL><THEAD ><TR ><TH >Function</TH ><TH >Return Type</TH ><TH >Description</TH ><TH >Example</TH ><TH >Result</TH ></TR ></THEAD ><TBODY ><TR ><TD ><CODE CLASS="FUNCTION" >hstore(record)</CODE ></TD ><TD ><TT CLASS="TYPE" >hstore</TT ></TD ><TD >construct an <TT CLASS="TYPE" >hstore</TT > from a record or row</TD ><TD ><TT CLASS="LITERAL" >hstore(ROW(1,2))</TT ></TD ><TD ><TT CLASS="LITERAL" >f1=>1,f2=>2</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >hstore(text[])</CODE ></TD ><TD ><TT CLASS="TYPE" >hstore</TT ></TD ><TD >construct an <TT CLASS="TYPE" >hstore</TT > from an array, which may be either a key/value array, or a two-dimensional array</TD ><TD ><TT CLASS="LITERAL" >hstore(ARRAY['a','1','b','2']) || hstore(ARRAY[['c','3'],['d','4']])</TT ></TD ><TD ><TT CLASS="LITERAL" >a=>1, b=>2, c=>3, d=>4</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >hstore(text[], text[])</CODE ></TD ><TD ><TT CLASS="TYPE" >hstore</TT ></TD ><TD >construct an <TT CLASS="TYPE" >hstore</TT > from separate key and value arrays</TD ><TD ><TT CLASS="LITERAL" >hstore(ARRAY['a','b'], ARRAY['1','2'])</TT ></TD ><TD ><TT CLASS="LITERAL" >"a"=>"1","b"=>"2"</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >hstore(text, text)</CODE ></TD ><TD ><TT CLASS="TYPE" >hstore</TT ></TD ><TD >make single-item <TT CLASS="TYPE" >hstore</TT ></TD ><TD ><TT CLASS="LITERAL" >hstore('a', 'b')</TT ></TD ><TD ><TT CLASS="LITERAL" >"a"=>"b"</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >akeys(hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >text[]</TT ></TD ><TD >get <TT CLASS="TYPE" >hstore</TT >'s keys as an array</TD ><TD ><TT CLASS="LITERAL" >akeys('a=>1,b=>2')</TT ></TD ><TD ><TT CLASS="LITERAL" >{a,b}</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >skeys(hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >setof text</TT ></TD ><TD >get <TT CLASS="TYPE" >hstore</TT >'s keys as a set</TD ><TD ><TT CLASS="LITERAL" >skeys('a=>1,b=>2')</TT ></TD ><TD ><PRE CLASS="PROGRAMLISTING" >a b</PRE ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >avals(hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >text[]</TT ></TD ><TD >get <TT CLASS="TYPE" >hstore</TT >'s values as an array</TD ><TD ><TT CLASS="LITERAL" >avals('a=>1,b=>2')</TT ></TD ><TD ><TT CLASS="LITERAL" >{1,2}</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >svals(hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >setof text</TT ></TD ><TD >get <TT CLASS="TYPE" >hstore</TT >'s values as a set</TD ><TD ><TT CLASS="LITERAL" >svals('a=>1,b=>2')</TT ></TD ><TD ><PRE CLASS="PROGRAMLISTING" >1 2</PRE ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >hstore_to_array(hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >text[]</TT ></TD ><TD >get <TT CLASS="TYPE" >hstore</TT >'s keys and values as an array of alternating keys and values</TD ><TD ><TT CLASS="LITERAL" >hstore_to_array('a=>1,b=>2')</TT ></TD ><TD ><TT CLASS="LITERAL" >{a,1,b,2}</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >hstore_to_matrix(hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >text[]</TT ></TD ><TD >get <TT CLASS="TYPE" >hstore</TT >'s keys and values as a two-dimensional array</TD ><TD ><TT CLASS="LITERAL" >hstore_to_matrix('a=>1,b=>2')</TT ></TD ><TD ><TT CLASS="LITERAL" >{{a,1},{b,2}}</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >slice(hstore, text[])</CODE ></TD ><TD ><TT CLASS="TYPE" >hstore</TT ></TD ><TD >extract a subset of an <TT CLASS="TYPE" >hstore</TT ></TD ><TD ><TT CLASS="LITERAL" >slice('a=>1,b=>2,c=>3'::hstore, ARRAY['b','c','x'])</TT ></TD ><TD ><TT CLASS="LITERAL" >"b"=>"2", "c"=>"3"</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >each(hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >setof(key text, value text)</TT ></TD ><TD >get <TT CLASS="TYPE" >hstore</TT >'s keys and values as a set</TD ><TD ><TT CLASS="LITERAL" >select * from each('a=>1,b=>2')</TT ></TD ><TD ><PRE CLASS="PROGRAMLISTING" > key | value -----+------- a | 1 b | 2</PRE ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >exist(hstore,text)</CODE ></TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >does <TT CLASS="TYPE" >hstore</TT > contain key?</TD ><TD ><TT CLASS="LITERAL" >exist('a=>1','a')</TT ></TD ><TD ><TT CLASS="LITERAL" >t</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >defined(hstore,text)</CODE ></TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >does <TT CLASS="TYPE" >hstore</TT > contain non-<TT CLASS="LITERAL" >NULL</TT > value for key?</TD ><TD ><TT CLASS="LITERAL" >defined('a=>NULL','a')</TT ></TD ><TD ><TT CLASS="LITERAL" >f</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >delete(hstore,text)</CODE ></TD ><TD ><TT CLASS="TYPE" >hstore</TT ></TD ><TD >delete pair with matching key</TD ><TD ><TT CLASS="LITERAL" >delete('a=>1,b=>2','b')</TT ></TD ><TD ><TT CLASS="LITERAL" >"a"=>"1"</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >delete(hstore,text[])</CODE ></TD ><TD ><TT CLASS="TYPE" >hstore</TT ></TD ><TD >delete pairs with matching keys</TD ><TD ><TT CLASS="LITERAL" >delete('a=>1,b=>2,c=>3',ARRAY['a','b'])</TT ></TD ><TD ><TT CLASS="LITERAL" >"c"=>"3"</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >delete(hstore,hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >hstore</TT ></TD ><TD >delete pairs matching those in the second argument</TD ><TD ><TT CLASS="LITERAL" >delete('a=>1,b=>2','a=>4,b=>2'::hstore)</TT ></TD ><TD ><TT CLASS="LITERAL" >"a"=>"1"</TT ></TD ></TR ><TR ><TD ><CODE CLASS="FUNCTION" >populate_record(record,hstore)</CODE ></TD ><TD ><TT CLASS="TYPE" >record</TT ></TD ><TD >replace fields in <TT CLASS="TYPE" >record</TT > with matching values from <TT CLASS="TYPE" >hstore</TT ></TD ><TD >see Examples section</TD ><TD > </TD ></TR ></TBODY ></TABLE ></DIV ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > The function <CODE CLASS="FUNCTION" >populate_record</CODE > is actually declared with <TT CLASS="TYPE" >anyelement</TT >, not <TT CLASS="TYPE" >record</TT >, as its first argument, but it will reject non-record types with a run-time error. </P ></BLOCKQUOTE ></DIV ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN148752" >F.16.3. Indexes</A ></H2 ><P > <TT CLASS="TYPE" >hstore</TT > has GiST and GIN index support for the <TT CLASS="LITERAL" >@></TT >, <TT CLASS="LITERAL" >?</TT >, <TT CLASS="LITERAL" >?&</TT > and <TT CLASS="LITERAL" >?|</TT > 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 > <TT CLASS="TYPE" >hstore</TT > also supports <TT CLASS="TYPE" >btree</TT > or <TT CLASS="TYPE" >hash</TT > indexes for the <TT CLASS="LITERAL" >=</TT > operator. This allows <TT CLASS="TYPE" >hstore</TT > columns to be declared <TT CLASS="LITERAL" >UNIQUE</TT >, or to be used in <TT CLASS="LITERAL" >GROUP BY</TT >, <TT CLASS="LITERAL" >ORDER BY</TT > or <TT CLASS="LITERAL" >DISTINCT</TT > expressions. The sort ordering for <TT CLASS="TYPE" >hstore</TT > values is not particularly useful, but these indexes may be useful for equivalence lookups. Create indexes for <TT CLASS="LITERAL" >=</TT > 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" ><H2 CLASS="SECT2" ><A NAME="AEN148774" >F.16.4. Examples</A ></H2 ><P > Add a key, or update an existing key with a new value: </P><PRE CLASS="PROGRAMLISTING" >UPDATE tab SET h = h || hstore('c', '3');</PRE ><P> </P ><P > Delete a key: </P><PRE CLASS="PROGRAMLISTING" >UPDATE tab SET h = delete(h, 'k1');</PRE ><P> </P ><P > Convert a <TT CLASS="TYPE" >record</TT > to an <TT CLASS="TYPE" >hstore</TT >: </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 <TT CLASS="TYPE" >hstore</TT > to a predefined <TT CLASS="TYPE" >record</TT > 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 <TT CLASS="TYPE" >hstore</TT >: </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" ><H2 CLASS="SECT2" ><A NAME="AEN148791" >F.16.5. Statistics</A ></H2 ><P > The <TT CLASS="TYPE" >hstore</TT > type, because of its intrinsic liberality, could contain a lot of different keys. Checking for valid keys is the task of the application. The following examples demonstrate several techniques for checking keys and obtaining statistics. </P ><P > Simple example: </P><PRE CLASS="PROGRAMLISTING" >SELECT * FROM each('aaa=>bq, b=>NULL, ""=>1');</PRE ><P> </P ><P > Using a table: </P><PRE CLASS="PROGRAMLISTING" >SELECT (each(h)).key, (each(h)).value INTO stat FROM testhstore;</PRE ><P> </P ><P > Online statistics: </P><PRE CLASS="PROGRAMLISTING" >SELECT key, count(*) FROM (SELECT (each(h)).key FROM testhstore) AS stat GROUP BY key ORDER BY count DESC, key; key | count -----------+------- line | 883 query | 207 pos | 203 node | 202 space | 197 status | 195 public | 194 title | 190 org | 189 ...................</PRE ><P> </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN148801" >F.16.6. Compatibility</A ></H2 ><P > As of PostgreSQL 9.0, <TT CLASS="TYPE" >hstore</TT > 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 <TT CLASS="LITERAL" >UPDATE</TT > 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 <TT CLASS="COMMAND" >ALTER TABLE</TT > method requires an exclusive lock on the table, but does not result in bloating the table with old row versions. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN148811" >F.16.7. Authors</A ></H2 ><P > Oleg Bartunov <CODE CLASS="EMAIL" ><<A HREF="mailto:oleg@sai.msu.su" >oleg@sai.msu.su</A >></CODE >, Moscow, Moscow University, Russia </P ><P > Teodor Sigaev <CODE CLASS="EMAIL" ><<A 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 HREF="mailto:andrew@tao11.riddles.org.uk" >andrew@tao11.riddles.org.uk</A >></CODE >, United Kingdom </P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="fuzzystrmatch.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="intagg.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >fuzzystrmatch</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="contrib.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >intagg</TD ></TR ></TABLE ></DIV ></BODY ></HTML >