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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="HSTORE"
>F.13. hstore</A
></H1
><A
NAME="AEN117055"
></A
><P
> This module implements a data type <TT
CLASS="TYPE"
>hstore</TT
> for storing sets of
(key,value) pairs within a single <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> data field.
This can be useful in various scenarios, such as rows with many attributes
that are rarely examined, or semi-structured data.
</P
><P
> In the current implementation, neither the key nor the value
string can exceed 65535 bytes in length; an error will be thrown if this
limit is exceeded. These maximum lengths may change in future releases.
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN117061"
>F.13.1. <TT
CLASS="TYPE"
>hstore</TT
> External Representation</A
></H2
><P
> The text representation of an <TT
CLASS="TYPE"
>hstore</TT
> value includes zero
or more <TT
CLASS="REPLACEABLE"
><I
>key</I
></TT
> <TT
CLASS="LITERAL"
>=></TT
> <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>
items, separated by commas. For example:
</P><PRE
CLASS="PROGRAMLISTING"
> k => v
foo => bar, baz => whatever
"1-a" => "anything at all"
</PRE
><P>
The order of the items is not considered significant (and may not be
reproduced on output). Whitespace between items or around the
<TT
CLASS="LITERAL"
>=></TT
> sign is ignored. Use double quotes if a key or
value includes whitespace, comma, <TT
CLASS="LITERAL"
>=</TT
> or <TT
CLASS="LITERAL"
>></TT
>.
To include a double quote or a backslash in a key or value, precede
it with another backslash. (Keep in mind that depending on the
setting of <TT
CLASS="VARNAME"
>standard_conforming_strings</TT
>, you may need to
double backslashes in SQL literal strings.)
</P
><P
> A value (but not a key) can be a SQL NULL. This is represented as
</P><PRE
CLASS="PROGRAMLISTING"
> key => NULL
</PRE
><P>
The <TT
CLASS="LITERAL"
>NULL</TT
> keyword is not case-sensitive. Again, use
double quotes if you want the string <TT
CLASS="LITERAL"
>null</TT
> to be treated
as an ordinary data value.
</P
><P
> Currently, double quotes are always used to surround key and value
strings on output, even when this is not strictly necessary.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN117079"
>F.13.2. <TT
CLASS="TYPE"
>hstore</TT
> Operators and Functions</A
></H2
><DIV
CLASS="TABLE"
><A
NAME="HSTORE-OP-TABLE"
></A
><P
><B
>Table F-5. <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 (null 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"
>text</TT
> <TT
CLASS="LITERAL"
>=></TT
> <TT
CLASS="TYPE"
>text</TT
></TD
><TD
>make single-item <TT
CLASS="TYPE"
>hstore</TT
></TD
><TD
><TT
CLASS="LITERAL"
>'a' => 'b'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"a"=>"b"</TT
></TD
></TR
><TR
><TD
><TT
CLASS="TYPE"
>hstore</TT
> <TT
CLASS="LITERAL"
>||</TT
> <TT
CLASS="TYPE"
>hstore</TT
></TD
><TD
>concatenation</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"
>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
></TBODY
></TABLE
></DIV
><P
> (Before PostgreSQL 8.2, the containment operators @> and <@ were
respectively called @ and ~. These names are still available, but are
deprecated and will eventually be retired. Notice that the old names
are reversed from the convention formerly followed by the core geometric
datatypes!)
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> The <TT
CLASS="LITERAL"
>=></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-6. <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(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 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 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 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 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"
>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 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-null 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 any item matching key</TD
><TD
><TT
CLASS="LITERAL"
>delete('a=>1,b=>2','b')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>"a"=>"1"</TT
></TD
></TR
></TBODY
></TABLE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN117270"
>F.13.3. Indexes</A
></H2
><P
> <TT
CLASS="TYPE"
>hstore</TT
> has index support for <TT
CLASS="LITERAL"
>@></TT
> and <TT
CLASS="LITERAL"
>?</TT
>
operators. You can use either GiST or GIN index types. For example:
</P
><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX hidx ON testhstore USING GIST(h);
CREATE INDEX hidx ON testhstore USING GIN(h);
</PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN117277"
>F.13.4. 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' => '3');
</PRE
><P
> Delete a key:
</P
><PRE
CLASS="PROGRAMLISTING"
>UPDATE tab SET h = delete(h, 'k1');
</PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN117283"
>F.13.5. 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. Examples below 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
> Using a table:
</P
><PRE
CLASS="PROGRAMLISTING"
>SELECT (each(h)).key, (each(h)).value INTO stat FROM testhstore;
</PRE
><P
> Online statistics:
</P
><PRE
CLASS="PROGRAMLISTING"
>SELECT key, count(*) FROM
(SELECT (each(h)).key FROM testhstore) AS stat
GROUP BY key
ORDER BY count DESC, key;
key | count
-----------+-------
line | 883
query | 207
pos | 203
node | 202
space | 197
status | 195
public | 194
title | 190
org | 189
...................
</PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN117293"
>F.13.6. 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
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