+++ /dev/null
-Hstore - contrib module for storing (key,value) pairs
-
-[Online version] (http://www.sai.msu.su/~megera/oddmuse/index.cgi?Hstore)
-
-Motivation
-
-Many attributes rarely searched, semistructural data, lazy DBA
-
-Authors
-
- * Oleg Bartunov <oleg@sai.msu.su>, Moscow, Moscow University, Russia
- * Teodor Sigaev <teodor@sigaev.ru>, Moscow, Delta-Soft Ltd.,Russia
-
-License
-
-Stable version, included into PostgreSQL distribution, released under BSD license. Development version, available from this site, released under the GNU General Public License, version 2 (June 1991).
-
-Operations
-
- * hstore -> text - get value , perl analogy $h{key}
-
-select 'a=>q, b=>g'->'a';
- ?
-------
- q
-
- * hstore || hstore - concatenation, perl analogy %a=( %b, %c );
-
-regression=# select 'a=>b'::hstore || 'c=>d'::hstore;
- ?column?
---------------------
- "a"=>"b", "c"=>"d"
-(1 row)
-
-but, notice
-
-regression=# select 'a=>b'::hstore || 'a=>d'::hstore;
- ?column?
-----------
- "a"=>"d"
-(1 row)
-
- * text => text - creates hstore type from two text strings
-
-select 'a'=>'b';
- ?column?
-----------
- "a"=>"b"
-
- * hstore @ hstore - contains operation, check if left operand contains right.
-
-regression=# select 'a=>b, b=>1, c=>NULL'::hstore @ 'a=>c';
- ?column?
-----------
- f
-(1 row)
-
-regression=# select 'a=>b, b=>1, c=>NULL'::hstore @ 'b=>1';
- ?column?
-----------
- t
-(1 row)
-
- * hstore ~ hstore - contained operation, check if left operand is contained in right
-
-Functions
-
- * akeys(hstore) - returns all keys from hstore as array
-
-regression=# select akeys('a=>1,b=>2');
- akeys
--------
- {a,b}
-
- * skeys(hstore) - returns all keys from hstore as strings
-
-regression=# select skeys('a=>1,b=>2');
- skeys
--------
- a
- b
-
- * avals(hstore) - returns all values from hstore as array
-
-regression=# select avals('a=>1,b=>2');
- avals
--------
- {1,2}
-
- * svals(hstore) - returns all values from hstore as strings
-
-regression=# select svals('a=>1,b=>2');
- svals
--------
- 1
- 2
-
- * delete (hstore,text) - delete (key,value) from hstore if key matches argument.
-
-regression=# select delete('a=>1,b=>2','b');
- delete
-----------
- "a"=>"1"
-
- * each(hstore) return (key, value) pairs
-
-regression=# select * from each('a=>1,b=>2');
- key | value
------+-------
- a | 1
- b | 2
-
- * isexists (hstore,text) - returns 'true if key is exists in hstore and false otherwise.
-
-regression=# select isexists('a=>1','a');
- isexists
-----------
- t
-
- * isdefined (hstore,text) - returns true if key is exists in hstore and its value is not NULL.
-
-regression=# select isdefined('a=>NULL','a');
- isdefined
------------
- f
-
-Indices
-
-Module provides index support for '@' and '~' operations.
-
-create index hidx on testhstore using gist(h);
-
-Note
-
-Use parenthesis in select below, because priority of 'is' is higher than that of '->'
-
-select id from entrants where (info->'education_period') is not null;
-
-Examples
-
- * add key
-
-update tt set h=h||'c=>3';
-
- * delete key
-
-update tt set h=delete(h,'k1');
-
- * Statistics
-
-hstore type, because of its intrinsic liberality, could contain a lot of different keys. Checking for valid keys is the task of application. Examples below demonstrate several techniques how to check keys statistics.
-
- o simple example
-
-select * from each('aaa=>bq, b=>NULL, ""=>1 ');
-
- o using table
-
-select (each(h)).key, (each(h)).value into stat from testhstore ;
-
- o online stat
-
-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
-...................
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