~ubuntu-branches/ubuntu/oneiric/postgresql-9.1/oneiric-security : contents of doc/src/sgml/html/hstore.html at revision 14

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><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="AEN134805"
>F.16.1. <TT
CLASS="TYPE"
>hstore</TT
> External Representation</A
></H2
><P
>&#13;   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"
>=&gt;</TT
>
   <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
> pairs separated by commas. Some examples:

</P><PRE
CLASS="SYNOPSIS"
>k =&gt; v
foo =&gt; bar, baz =&gt; whatever
"1-a" =&gt; "anything at all"</PRE
><P>

   The order of the pairs is not significant (and may not be reproduced on
   output). Whitespace between pairs or around the <TT
CLASS="LITERAL"
>=&gt;</TT
> sign is
   ignored. Double-quote keys and values that include whitespace, commas,
   <TT
CLASS="LITERAL"
>=</TT
>s or <TT
CLASS="LITERAL"
>&gt;</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=&gt;1,a=&gt;2'::hstore;
  hstore
----------
 "a"=&gt;"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 =&gt; 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="AEN134836"
>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-6</A
>, the functions
   in <A
HREF="hstore.html#HSTORE-FUNC-TABLE"
>Table F-7</A
>.
  </P
><DIV
CLASS="TABLE"
><A
NAME="HSTORE-OP-TABLE"
></A
><P
><B
>Table F-6. <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"
>-&gt;</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=&gt;x, b=&gt;y'::hstore -&gt; 'a'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>x</TT
></TD
></TR
><TR
><TD
><TT
CLASS="TYPE"
>hstore</TT
> <TT
CLASS="LITERAL"
>-&gt;</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=&gt;x, b=&gt;y, c=&gt;z'::hstore -&gt; ARRAY['c','a']</TT
></TD
><TD
><TT
CLASS="LITERAL"
>{"z","x"}</TT
></TD
></TR
><TR
><TD
><TT
CLASS="TYPE"
>text</TT
> <TT
CLASS="LITERAL"
>=&gt;</TT
> <TT
CLASS="TYPE"
>text</TT
></TD
><TD
>make single-pair <TT
CLASS="TYPE"
>hstore</TT
></TD
><TD
><TT
CLASS="LITERAL"
>'a' =&gt; 'b'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"a"=&gt;"b"</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=&gt;b, c=&gt;d'::hstore || 'c=&gt;x, d=&gt;q'::hstore</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"a"=&gt;"b", "c"=&gt;"x", "d"=&gt;"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=&gt;1'::hstore ? 'a'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>t</TT
></TD
></TR
><TR
><TD
><TT
CLASS="TYPE"
>hstore</TT
> <TT
CLASS="LITERAL"
>?&amp;</TT
> <TT
CLASS="TYPE"
>text[]</TT
></TD
><TD
>does <TT
CLASS="TYPE"
>hstore</TT
> contain all specified keys?</TD
><TD
><TT
CLASS="LITERAL"
>'a=&gt;1,b=&gt;2'::hstore ?&amp; 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=&gt;1,b=&gt;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"
>@&gt;</TT
> <TT
CLASS="TYPE"
>hstore</TT
></TD
><TD
>does left operand contain right?</TD
><TD
><TT
CLASS="LITERAL"
>'a=&gt;b, b=&gt;1, c=&gt;NULL'::hstore @&gt; 'b=&gt;1'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>t</TT
></TD
></TR
><TR
><TD
><TT
CLASS="TYPE"
>hstore</TT
> <TT
CLASS="LITERAL"
>&lt;@</TT
> <TT
CLASS="TYPE"
>hstore</TT
></TD
><TD
>is left operand contained in right?</TD
><TD
><TT
CLASS="LITERAL"
>'a=&gt;c'::hstore &lt;@ 'a=&gt;b, b=&gt;1, c=&gt;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=&gt;1, b=&gt;2, c=&gt;3'::hstore - 'b'::text</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"a"=&gt;"1", "c"=&gt;"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=&gt;1, b=&gt;2, c=&gt;3'::hstore - ARRAY['a','b']</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"c"=&gt;"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=&gt;1, b=&gt;2, c=&gt;3'::hstore - 'a=&gt;4, b=&gt;2'::hstore</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"a"=&gt;"1", "c"=&gt;"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
>&nbsp;</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=&gt;foo, b=&gt;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=&gt;foo, b=&gt;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"
>@&gt;</TT
>
   and <TT
CLASS="LITERAL"
>&lt;@</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="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>   The <TT
CLASS="LITERAL"
>=&gt;</TT
> operator is deprecated and may be removed in a
   future release.  Use the <TT
CLASS="LITERAL"
>hstore(text, text)</TT
> function
   instead.
   </P
></BLOCKQUOTE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="HSTORE-FUNC-TABLE"
></A
><P
><B
>Table F-7. <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=&gt;1,f2=&gt;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=&gt;1, b=&gt;2, c=&gt;3, d=&gt;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"=&gt;"1","b"=&gt;"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"=&gt;"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=&gt;1,b=&gt;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=&gt;1,b=&gt;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=&gt;1,b=&gt;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=&gt;1,b=&gt;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=&gt;1,b=&gt;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=&gt;1,b=&gt;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=&gt;1,b=&gt;2,c=&gt;3'::hstore, ARRAY['b','c','x'])</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"b"=&gt;"2", "c"=&gt;"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=&gt;1,b=&gt;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=&gt;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=&gt;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=&gt;1,b=&gt;2','b')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"a"=&#62;"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=&gt;1,b=&gt;2,c=&gt;3',ARRAY['a','b'])</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"c"=&#62;"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=&gt;1,b=&gt;2','a=&gt;4,b=&gt;2'::hstore)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"a"=&#62;"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
>&nbsp;</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="AEN135233"
>F.16.3. Indexes</A
></H2
><P
>   <TT
CLASS="TYPE"
>hstore</TT
> has GiST and GIN index support for the <TT
CLASS="LITERAL"
>@&gt;</TT
>,
   <TT
CLASS="LITERAL"
>?</TT
>, <TT
CLASS="LITERAL"
>?&amp;</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="AEN135255"
>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 || ('c' =&gt; '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"=&gt;"123", "col2"=&gt;"foo", "col3"=&gt;"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"=&gt;"456", "col2"=&gt;"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"=&gt;"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="AEN135272"
>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=&gt;bq, b=&gt;NULL, ""=&gt;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="AEN135282"
>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="AEN135292"
>F.16.7. Authors</A
></H2
><P
>   Oleg Bartunov <CODE
CLASS="EMAIL"
>&#60;<A
HREF="mailto:oleg@sai.msu.su"
>oleg@sai.msu.su</A
>&#62;</CODE
>, Moscow, Moscow University, Russia
  </P
><P
>   Teodor Sigaev <CODE
CLASS="EMAIL"
>&#60;<A
HREF="mailto:teodor@sigaev.ru"
>teodor@sigaev.ru</A
>&#62;</CODE
>, Moscow, Delta-Soft Ltd., Russia
  </P
><P
>   Additional enhancements by Andrew Gierth <CODE
CLASS="EMAIL"
>&#60;<A
HREF="mailto:andrew@tao11.riddles.org.uk"
>andrew@tao11.riddles.org.uk</A
>&#62;</CODE
>,
   United Kingdom
  </P
></DIV
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