现在满地都是KV数据库的文字，PostgreSQL 也有类似的结构。不过是通过其强大的扩展方式实现的。
官网文档请参考：http://www.postgresql.org/docs/current/static/hstore.html
本文测试环境在 Mac OS 下，Pg采用源码编译。
编译 hstore 扩展
mac:~ smallfish$ cd Downloads/postgresql-9.0.1/contrib/hstore/
mac:hstore smallfish$ make
... 一堆编译信息
mac:hstore smallfish$ sudo make install
导入到数据库中，注意必须以 postgres 用户，如果需要装入到指定数据库，请指明。这里采用默认数据库。
mac:hstore smallfish$ ls /opt/postgresql/share/contrib/
hstore.sql uninstall_hstore.sql
mac:hstore smallfish$ psql -U postgres -f /opt/postgresql/share/contrib/hstore.sql
... 一堆导入命令
进入数据库，建一个测试表
postgres=# CREATE TABLE testhstore (id SERIAL, value hstore);
NOTICE: CREATE TABLE will create implicit sequence "testhstore_id_seq" for serial column "testhstore.id"
CREATE TABLE
查看下表结构
postgres=# d
List of relations
Schema | Name | Type | Owner
--------+-------------------+----------+----------
public | testhstore | table | postgres
public | testhstore_id_seq | sequence | postgres
(2 rows)
postgres=# d testhstore;
Table "public.testhstore"
Column | Type | Modifiers
--------+---------+---------------------------------------------------------
id | integer | not null default nextval('testhstore_id_seq'::regclass)
value | hstore |
尝试下简单 hstore类型
postgres=# select 'a=>1, b=>2'::hstore;
hstore
--------------------
"a"=>"1", "b"=>"2"
(1 row)
postgres=# select 'a=>1, b=>a'::hstore;
hstore
--------------------
"a"=>"1", "b"=>"a"
(1 row)
写几条测试数据先
postgres=# INSERT INTO testhstore (value) VALUES ('name=>smallfish, age=>29'::hstore);
INSERT 0 1
postgres=# SELECT * FROM testhstore;
id | value
----+----------------------------------
1 | "age"=>"29", "name"=>"smallfish"
(1 row)
postgres=# INSERT INTO testhstore (value) VALUES ('name=>nnfish, age=>20'::hstore);
INSERT 0 1
postgres=# INSERT INTO testhstore (value) VALUES ('name=>aaa, age=>30, addr=>China'::hstore);
INSERT 0 1
查看下所有数据
postgres=# SELECT * FROM testhstore;
id | value
----+---------------------------------------------
1 | "age"=>"29", "name"=>"smallfish"
2 | "age"=>"20", "name"=>"nnfish"
3 | "age"=>"30", "addr"=>"China", "name"=>"aaa"
(3 rows)
查询列里面的指定 key
postgres=# SELECT id, value->'name' AS name FROM testhstore;
id | name
----+-----------
1 | smallfish
2 | nnfish
3 | aaa
(3 rows)
postgres=# SELECT id, value->'name', value->'age' AS age FROM testhstore;
id | ?column? | age
----+-----------+-----
1 | smallfish | 29
2 | nnfish | 20
3 | aaa | 30
(3 rows)
修改列某 key 值
postgres=# UPDATE testhstore SET value=value||('addr=>Shanghai') WHERE id = 2;
UPDATE 1
postgres=# SELECT * FROM testhstore;
id | value
----+---------------------------------------------------
1 | "age"=>"29", "name"=>"smallfish"
3 | "age"=>"30", "addr"=>"China", "name"=>"aaa"
2 | "age"=>"20", "addr"=>"Shanghai", "name"=>"nnfish"
(3 rows)
删除列里某 key
postgres=# UPDATE testhstore SET value=delete(value, 'addr') WHERE id = 3;
UPDATE 1
postgres=# SELECT * FROM testhstore;
id | value
----+---------------------------------------------------
1 | "age"=>"29", "name"=>"smallfish"
2 | "age"=>"20", "addr"=>"Shanghai", "name"=>"nnfish"
3 | "age"=>"30", "name"=>"aaa"
(3 rows)
按条件查询列里某 key ，注意要数据类型，CAST 强转。默认都是字符串的值。
postgres=# SELECT * FROM testhstore WHERE (value->'age')::INT > 20;
id | value
----+----------------------------------
1 | "age"=>"29", "name"=>"smallfish"
3 | "age"=>"30", "name"=>"aaa"
(2 rows)
postgres=# SELECT * FROM testhstore WHERE value->'name' = 'smallfish';
id | value
----+----------------------------------
1 | "age"=>"29", "name"=>"smallfish"
(1 row)